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This is the free full text of AppSurgeOn - 3D Skull Atlas.

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Ethmoid Bone

The ethmoid bone lies in the middle of the anterior skull base and forms part of the medial walls of the orbits, part of the nasal septum, and the roof and lateral walls of the nasal cavities. It is irregularly cuboidal shaped, composed of a horizontal perforated cribriform plate, a median perpendicular plate, and two lateral labyrinths containing the ethmoidal air cells. It articulates with the frontal, sphenoid, maxillary, palatine, inferior concha, vomer, nasal, and lacrimal bones.

 

Full Description

PARTS
Cribriform plate

The upper surface of the cribriform plate is divided by a median process, called the crista galli. Two crista galli alae arise from the anterior part of the crista galli, and the notch that contributes to the foramen caecum is situated between them, on the anterior surface of the crista galli. The anterior ethmoidal foramina are located lateral to the crista galli on both sides of the cribriform plate. Two grooves, housing the meningeal branch of the anterior ethmoidal arteries, extend on the two sides from the anterior ethmoidal foramina towards the foramen caecum.

Ethmoidal labyrinths

It contains the ethmoidal air cells, which, from a surgical point of view, are subdivided into anterior and posterior cells by the basal lamella of the middle concha. The anterior cells drain into the middle nasal meatus, while the posterior cells drain into the superior meatus. In vivo, many air cells’ walls are constituted by adjacent bones, such as the sphenoid conchae, the orbital process of the palatine bone, the lacrimal bone, and the frontal process of the maxillary bone. Each labyrinth is roofed by the fovea ethmoidalis of the frontal bone. Therefore, the air cells are superiorly open in the isolated ethmoid bone. The anterior and posterior ethmoidal grooves are likewise visible on the superior surface of the ethmoidal labyrinths. The frontal sinus drainage pathway, which allows the content of the frontal sinus to drain into the nasal cavity, is also evident superiorly, as it connects the frontal sinus to the middle nasal meatus. 
The lamina papyracea forms the lateral wall of the labyrinth on each side.
The ethmoid bulla, the uncinate process, the middle nasal concha, and the superior nasal concha are visible on the medial side of the labyrinths. The ethmoid bulla and the uncinate process are separated by the narrow hiatus semilunaris, which gives access to the ethmoid infundibulum.

Perpendicular plate

It descends from the inferior surface of the cribriform plate approximately in the midsagittal plane, although it typically deviates slightly from the midline.

ARTICULATIONS

The ethmoid bone articulates with the frontal, sphenoid, maxillary, palatine, inferior concha, vomer, nasal, and lacrimal bones. 

Anatomical Details

Anterior Ethmoidal Foramen

The foramen that transmits the anterior ethmoidal nerve and vessels to the nasal cavity. It is located anteroinferiorly on each side of the crista galli.

 

Anterior Ethmoidal Groove

Ethmoidal part of the anterior ethmoidal canal formed with the corresponding groove of the frontal bone. It carries the anterior ethmoidal artery.

 

Anterior Falcine Artery Groove

The groove for the meningeal branch of the anterior ethmoidal artery, which continues as anterior falcine artery. It runs from the anterior ethmoidal canal posteriorly to the foramen caecum anteriorly.

 

Cribriform Plate

The median, horizontal, perforated plate that constitutes part of the nasal roof, located in the ethmoidal notch of the frontal bone. The posterior portion of the cribriform plate is wider and less depressed than the anterior one. Its name reflects the presence of numerous foramina allowing branches of the olfactory nerves to reach the nasal cavities.

 

Crista Galli

Thick triangular process, located in the midsagittal plane, which arises from the anterior part of the cribriform plate. It extends upwards to give insertion to the falx cerebri, in particular with its curved posterior edge. Two small alae are visible on its anterior border. The crista galli may be pneumatized, showing bulges on its sides, which, instead, are typically smooth.

 

Crista Galli Ala

Small eminence on each side of the anterior border of the crista galli that articulates with the frontal bone constituting the foramen caecum.

 

Ethmoid Bulla

Bone swelling on the lateral wall of the middle meatus produced by middle ethmoidal air cells, which open into the middle meatus.

 

Ethmoid Infundibulum

Space bound by the uncinate process anteromedially, the ethmoid bulla posterolaterally, and the lamina papyracea anterolaterally. It extends anterosuperiorly from the middle meatus and communicates with the anterior ethmoidal sinuses. The terminal recess of the infundibulum is present if the upper end of the uncinate process reaches the lamina papyracea and not the skull base.

 

Ethmoidal Air Cells

The air cells of the Ethmoid bone are anatomically arranged into anterior, middle and posterior groups. From a surgical point of view, the air cells are subdivided in anterior and posterior cells by the basal lamella of the middle concha. In the disarticulated bone, many air cells are open, but in life, and in the articulated skull, they are closed by proximity to adjoining bones, except where they open into the nasal cavity.

 

Foramen Caecum Notch

Small notch completed by the corresponding notch of the frontal bone to form the Foramen Caecum.

 

Frontal Sinus Drainage Pathway

The narrow space in which the ostium of the frontal sinus opens. It is formed by the ethmoid infundibulum when the uncinate process reaches the skull base, while it corresponds to the middle meatus when the uncinate process inserts on the lamina papyracea.

 

Hiatus Semilunaris

Narrow passage between the uncinate process and the ethmoid bulla, through which the ethmoid infundibulum communicates with the middle meatus.

 

Lamina Papyracea

Lateral, vertical surface of the ethmoidal labyrinth. It is part of the medial orbital wall.

 

Middle Nasal Concha

Thin, convex lamella extending along the entire medial surface of the labyrinth, anteroinferior to the superior meatus. Its lower edge is thick, and its lateral surface is concave and forms part of the middle meatus.

 

Perpendicular plate

Thin, quadrilateral process that descends from the cribriform plate to form the upper part of the nasal septum. Although it is described to lay in the midsagittal plane, it usually deviates slightly from the midline. Its superior portion shows numerous grooves that carry medial filaments of the olfactory nerves.

 

Posterior Ethmoidal Groove

The ethmoidal part of the posterior ethmoidal canal formed with the corresponding groove of the frontal bone. It carries the posterior ethmoidal artery.

 

Superior Nasal Concha

Curved, thin lamella located posterosuperior to the basal lamella of the middle turbinate. It is visible in the posterosuperior portion of the medial surface of the ethmoidal labyrinth, and it bounds medially and superiorly the superior meatus.

 

Uncinate Process

A thin, curved process of a variable size, which projects posteroinferiorly from the labyrinth. Its upper edge constitutes the anterior boundary of the hiatus semilunaris in the middle meatus. The uncinate process  crosses the maxillary hiatus to articulate with the ethmoidal process of the inferior nasal concha.

 

 

Frontal Bone

The frontal bone forms the main part of the forehead, part of the orbital roofs, part of the anterior cranial fossa, and part of the nose. It is irregularly semicircular shaped superiorly, with two posterior flat projections constituting the orbital roofs inferiorly. The frontal bone can be divided into three portions: the squamous part, the nasal part, and the orbital part. Furthermore, it contains two cavities, called frontal sinuses, and articulates with the parietal, ethmoid, sphenoid, nasal, maxillary, lacrimal, and zygomatic bones.

 

Full Description

PARTS
Nasal part

It is the part situated between the supraorbital margins, presenting the nasal notch inferiorly, where it articulates with the nasal bones. The nasal notch is subdivided by the inferiorly projecting nasal spine. The inferior portions of the frontal sinuses are contained between the plates of bone of the nasal part. A thin septum, typically not located in the median plane, separates asymmetrically the two sinuses. The openings of the frontal sinuses are located in the floor of the nasal part, anterior to the ethmoidal notch and lateral to the nasal spine.

Orbital part

It is composed of two inferiorly concave, triangular plates projecting posteriorly above the orbits. The inferior surface presents the lacrimal fossa in its anterolateral portion, while the trochlear spine arises from the anteromedial portion, being located posteroinferior to the medial end of the supraorbital margin and halfway between the supraorbital notch and the fronto-lacrimal suture. The medial portion of each orbital plate, marked by impressions of the ethmoidal air cells, constitutes the fovea ethmoidalis, and the space between them is called the ethmoidal notch. The fovea ethmoidalis is grooved by two sulci that complete the anterior and posterior ethmoidal canals. The superior surface is marked by impressions of cerebral gyri and small grooves for meningeal vessels. The orbital plates may be partly absorbed in the elderly.

Squamous part

Its external surface is occupied mostly by the frontal tuberosity. The glabella is located inferior to the tuberosity, contained between the superciliary arches, and it is furrowed by traces of the metopic (or inter-frontal) suture in 9% of cases. The supraorbital margins, located below the superciliary arches, edge the orbital cavities, and are pierced or grooved by the supraorbital foramen, or notch, respectively. The frontal notch, or foramen, can also be present medial to the supraorbital one. The zygomatic process is located lateral to the supraorbital margin. The temporal line arises from this process and directs posteriorly, lateral to the frontal tuberosity, dividing eventually into superior and inferior temporal lines. 
The internal surface is marked by impressions of cerebral gyri and small grooves for meningeal vessels. It shows a median frontal crest, grooved by the notch that completes the foramen caecum, and by the sulcus for the superior sagittal sinus. Next to the sinus, the granular foveolae can be observed. The frontal sinuses extend irregularly into the squamous part, being usually larger in males and extending accordingly to the prominence of the superciliary arches. They complete their growth after puberty, being undeveloped at birth and radiographically detectable after the fifth year. They can increase in size in the elderly due to bone reabsorption.

ARTICULATIONS

The frontal bone articulates with the parietal, ethmoid, sphenoid, nasal, maxillary, lacrimal, and zygomatic bones. 

SKELETAL LANDMARKS

The supraorbital margin can be palpated above the eye, deep to the eyebrow. The supraorbital and frontal notches or foramina can be found along its ridge. The superciliary arch is located immediately above the supraorbital margin; while the frontal tuberosity is approximately 3 cm above its midpoint. The glabella is palpable between the superciliary arches, along with the nasion depression inferior to it. The lateral borders of the orbits are defined by the zygomatic processes, articulating with the frontal processes of the zygomatic bones. The fronto-zygomatic suture is located approximately 3 cm anterior to the pterion, which marks the Sylvian point and overlies the frontal branch of the middle meningeal artery.

Anatomical Details

Anterior Ethmoidal Groove

The groove that completes the corresponding notch on the ethmoid bone to constitute the anterior ethmoidal canal, which is traversed by the anterior ethmoidal nerve and vessels.

 

Ethmoidal Notch

The quadrangular space between the two orbital plates of the frontal bone. It is occupied by the cribriform plate of the ethmoid bone.

 

Foramen Caecum Notch

Small notch on the frontal crest that is completed by the corresponding notch on the ethmoid bone, to form the foramen caecum.

 

Fovea Ethmoidalis

The medial portion of the orbital plate, which constitutes the roof of the ethmoid labyrinth. Its surface shows impressions of the ethmoidal air cells.

 

Frontal Crest

Median crest on the internal surface of the frontal bone. It presents a sulcus for the superior sagittal sinus.

 

Frontal Notch

The frontal notch, or foramen, is a small indentation medial to the supraorbital notch. It is present in 50% of skulls, and carries the supratrochlear vessels and nerve.

 

Frontal Sinus Opening

The opening of the frontal sinus, located below the sinus, that continues as the frontal sinus drainage pathway inside the ethmoid bone.

 

Frontal Tuberosity

Rounded eminence on the external surface of the frontal bone. It is more evident in females.

 

Glabella

Median smooth elevation located between the superciliary arches.

 

Granular Foveola

Granular foveolae can be seen lateral to the sulcus for the superior sagittal sinus. They lodge the arachnoid granulations.

 

Inferior Temporal Line

Inferior ridge derived from the division of the temporal line of the frontal bone. It continues on the parietal bone.

 

Lacrimal Fossa

Small depression located in the anterolateral portion of the orbital surface of the frontal bone lodging the lacrimal gland.

 

Nasal Spine

Median prominence projecting inferiorly from the nasal notch in the midsagittal plane. It makes a small contribution to the anterosuperior part of the nasal septum.

 

Posterior Ethmoidal Groove

The groove that completes the corresponding notch on the ethmoid bone to constitute the posterior ethmoidal canal, which is traversed by the posterior ethmoidal nerve and vessels.

 

Superciliary Arch

Prominence located below the frontal tuberosity and above the supraorbital margin. It is more evident in males and, although it usually reflects the size of the frontal sinus, it is occasionally associated with a small sinus.

 

Superior Sagittal Sinus Sulcus

A wide sulcus with raised edges that reaches the frontal crest on the frontal bone, continues for the entire length of the parietal bones (with half of the sulcus on both parietal bones), and extends from the lambdoid suture to the internal occipital protuberance on the occipital bone. Its edges give attachment to the falx cerebri.

 

Superior Temporal Line

Superior ridge derived from the division of the temporal line of the frontal bone. It continues on the parietal bone.

 

Supraorbital Foramen

The supraorbital foramen, or notch, is located between the sharp and the smooth portions of the supraorbital margin. It contains the supraorbital vessels and nerve.

 

Supraorbital Margin

Superior edge of the orbital cavity. It is visible below the superciliary arches, showing sharp lateral two-thirds, and a rounded medial third.

 

Temporal Line

Curved ridge directed posterosuperiorly from the zygomatic process. It divides into superior and inferior temporal lines.

 

Trochlear Spine

Small spicule located behind and below the medial end of the supraorbital margin. It is located halfway between the fronto-lacrimal suture and the supraorbital notch. It gives attachment to the trochlea of the superior oblique muscle.

 

Zygomatic Process

The process that extends inferiorly to articulate with the zygomatic bone. It is the inferolateral continuation of the supraorbital margin.

 

Inferior Nasal Concha Bone

The inferior nasal concha bone constitutes the bone of the inferior turbinate and part of the medial wall of the maxillary sinus. It is a curved, horizontal lamina with two surfaces (medial and lateral) and cone-shaped anterior and posterior ends, the posterior being sharper. It articulates with the maxillary, ethmoid, and palatine bones.

 

Full Description

SHAPE

The inferior nasal concha bone constitutes the bone of the inferior turbinate and part of the medial wall of the maxillary sinus. It is a curved, horizontal lamina with two surfaces (medial and lateral) and cone-shaped anterior and posterior ends, the posterior being sharper. The medial surface is convex and shows grooves and holes for vessels, while the lateral surface is convex. The inferior border is thick, especially in its middle portion.

PARTS
Anterior segment

It is the part articulating with the conchal crest of the maxillary bone.

Middle segment

It is the part located medial to the maxillary hiatus of the maxillary bone. It presents the lacrimal, ethmoidal, and maxillary processes arising from its upper border.

Posterior segment

It is the part articulating with the conchal crest of the palatine bone.

ARTICULATIONS

The inferior nasal concha bone articulates with the maxillary, ethmoid, and palatine bones. 

Anatomical Details

Ethmoidal Process

The most posterior of the three processes of the inferior nasal concha. It is thin and directed superiorly to meet the uncinate process of the ethmoid bone.

 

Lacrimal Process

The most anterior of the three processes of the inferior nasal concha. It is small, pointed, and directed anteriorly to complete the nasolacrimal canal.

 

Maxillary Process

The process located between the other two processes of the inferior nasal concha. It curves inferolaterally to articulate with the medial surface of the maxilla at the maxillary hiatus.

 

Lacrimal Bone

The lacrimal bone forms part of the medial wall of the orbit and part of the lacrimal fossa. It has two surfaces and four borders, and articulates with the frontal, maxillary, ethmoid, and inferior concha bones.

 

Full Description

 
PARTS
Nasal surface

It is marked posterosuperiorly by some of the anterior ethmoidal cells, which are completed by the the lacrimal bone.

Orbital surface

It is subdivided vertically by the posterior lacrimal crest. The groove for the lacrimal sac, completed by the corresponding one on the maxillary bone, is located anterior to the crest. The bone of the groove extends inferiorly, contributing to the formation of the nasolacrimal canal, which is completed by the maxillary bone and the lacrimal process of the inferior nasal concha. The lacrimal hamulus arises laterally from the inferior border of the lacrimal bone.

ARTICULATIONS

The lacrimal bone articulates with the frontal, maxillary, ethmoid, and inferior concha bones. 

Anatomical Details

Lacrimal Hamulus

Hook-like projection on the inferior edge of the lacrimal bone. It articulates with the maxilla completing the upper opening of the nasolacrimal canal. The hamulus may appear as a separate lesser lacrimal bone.

 

Lacrimal Sac Groove

Vertical groove anterior to the vertical crest. Together with the frontal process of the maxillary bone, it forms a fossa that contains the lacrimal sac.

 

Posterior Lacrimal Crest

Vertical crest that divides the lateral (orbital) surface of the lacrimal bone.

 

Mandible Bone

The mandible bone (jawbone) is the largest and the lowest bone of the face. It is composed of an anteriorly convex horizontal body and two posterior superiorly directed rami. The body has external and internal surfaces separated by upper and lower borders. The mandibular ramus is quadrilateral, and has two surfaces (lateral and medial), four borders (superior, inferior, anterior and posterior) and two processes (coronoid and condylar). The inferior alveolar process, that contains the roots of the inferior teeth, arises superiorly from the body of the mandible. The mandible articulates with the ipsilateral temporal bone constituting the temporo-mandibular joints, in which mandibular fossae of the temporal bones lodge the condyles of the mandible.

 

Full Description

PARTS
Body of the mandible

Its external surface is marked by the ridge corresponding to the fused symphysis menti and the mental protuberance in the median plane. Two mental tubercles are present on both sides of the mental protuberance, constituting the chin together with the protuberance. The mental foramen can be located below the apex of the second premolar tooth in 74.5% of cases, or below the space between the premolar teeth, and halfway between the upper and the lower borders of the body of the mandible. An external oblique line arises from the mental tubercle and continues as the anterior border of the ramus of the mandible, passing below the mental foramen on both sides. The inferior border of the body extends bilaterally in a posterolateral direction from the mandibular symphysis, and continues behind the third molar tooth into the inferior border of the ramus of the mandible. It shows a digastric fossa near the midline, and it is anteroposteriorly convex, thick, and rounded posterior to this fossa. A slight concavity appears posterior to the convexity where the body turns into the ramus. Therefore, the inferior border of the body of the mandible has an overall sinuous profile. 
The internal surface is grooved by the mylohyoid line, from behind the third molar tooth to the mental symphysis, and by the mylohyoid groove, from the ramus of the mandible to the area below the mylohyoid line. The submandibular fossa, sublingual fossa, and torus mandibularis are visible on the internal surface. The mental spines (or genial tubercles) are situated above the anterior ends of the mylohyoid lines, and a lingual (or genial) foramen can be present superior to them.

Alveolar process

The process constituting the superior border of the mandible. It is composed of buccal and lingual plates, as well as interdental and inter-radicular septa.

Condylar process

Ovoid-shaped process, composed of cancellous bone and covered by compact bone, that is coated with fibrocartilage on its intra-articular surface in order to articulate with the mandibular fossa of the temporal bone. Its medial aspect is wider than the lateral one. The process is connected to the ramus of the mandible through the neck of the condyle. The pterygoid fovea is present on the anterior aspect of the neck. The condylar process gives insertion to the lateral pterygoid muscle.

Coronoid process

Triangular, flat plate of bone projecting anterosuperiorly. Its posterior border contributes to the mandibular incisure, whereas its anterior one is continuous with the anterior edge of the ramus. It gives insertion to the temporal muscle.

Ramus of the mandible

Its medial surface presents the mandibular foramen and the lingula, anteromedial to the foramen. The mandibular foramen gives access to the mandibular canal. It runs anteroinferiorly inside the ramus and almost horizontally within the body, being enclosed by trabecular bone or a thin layer of cortical bone. It shows small foramina for the branches directed to the molar teeth. At the level of the mental foramen, the mental neurovascular bundle leaves the mandibular canal, while the incisor nerve and vessels remain within the bone to supply the anterior teeth. The posterior end of the mylohyoid groove is located inferoposterior to the mandibular foramen. The temporal crest runs from behind the third molar tooth to the tip of the coronoid process. 
The medial surface gives insertion to the medial pterygoid muscle. The lateral surface is marked only by the ending of the external oblique line, and gives insertion to the masseter muscle. The anterior border is thin superiorly, where the coronoid process arises, while it is thicker inferiorly, where it joins the external oblique line. The retromolar fossa is present between the external oblique line and the temporal crest. The rounded, thick posterior border is slight concave inferiorly and convex superiorly. It turns into the inferior border at the level of the angle of the mandible. The superior border of the ramus shows the mandibular incisure and the condylar and coronoid processes.

ARTICULATIONS

The mandible bone articulates with the ipsilateral temporal bone constituting the temporo-mandibular joints, in which the mandibular fossae of the temporal bones lodge the condyles of the mandible.

SKELETAL LANDMARKS

The line connecting the mental tubercles and the angle of the mandible indicates the level of C2 vertebra. The mental foramen is located approximately one finger above the inferior border of the body of the mandible and two fingers lateral to the midsagittal plane. Its vertical plane is almost the same of the infraorbital and supraorbital foramina. The lobule of the ear overlies the neck of the condylar process.

Anatomical Details

Alveolar Process

Upper part of the body of the mandible. It contains the alveoli for the inferior teeth.

 

Alveolus

Cavity in the alveolar process that houses a tooth. 16 alveoli for the inferior teeth are present in total.

 

Buccal Plate

Thin lamella of bone that constitutes the wall of the alveoli towards the vestibule of the mouth.

 

Condylar Process

Ovoid-shaped process composed of cancellous bone, covered by compact bone, that shows fibrocartilage on its intra-articular surface in order to articulate with the mandibular fossa of the temporal bone. Its medial aspect is wider than the lateral one. Anteroposteriorly, its is about half its latero-medial dimension wide, with its long axis diverging posteromedially from the coronal plane. Therefore, the medial pole of the condyle lies slightly posterior to the lateral pole. Extending the long axes of the two condyles, they intersect with an obtuse angle (about 145°) at the anterior border of the foramen magnum. The condylar process gives insertion to the lateral pterygoid muscle.

 

Condylar Process Neck

Segment located between the ramus of the mandible and the articular head of the condyle.

 

Condyle Articular Surface

The intra-articular surface of the condyle which articulates with the mandibular fossa of the temporal bone. It is covered with fibrocartilage and comes in contact with the articular disc of the temporo-mandibular joint.

 

Coronoid Process

Triangular, flat plate of bone projecting anterosuperiorly. Its posterior border contributes to the mandibular incisure, and its anterior one is continuous with the anterior edge of the ramus. It gives insertion to the temporal muscle.

 

Digastric Fossa

Irregular depression located near the midline of the mandible body. It gives attachment to the anterior belly of the digastric muscle.

 

External Oblique Line

Line originating from the mental tubercle of the mandible and directed posterosuperiorly. It is faint anteriorly, although it becomes more marked where it continues into the anterior border of the ramus of the mandible. It crosses the mental foramen passing below it and overlaps the buccal plate near the second and third molar teeth.

 

Interdental Septum

Lamella of bone that separates two alveoli, connecting the buccal and the lingual plates.

 

Inter-radicular Septum

Lamella of bone that separates the roots of the tooth in each alveolus. The number of septa in each alveolus changes according to the number of roots of its tooth. The incisive, canine and premolar teeth usually have one root, while the three molar teeth show two or three roots.

 

Lingual Foramen

A foramen that can be present above the mental spines and opens into a canal as long as the 50% of the anteroposterior depth of the mandible. It contains a branch of the lingual artery, arising from the sublingual branch. Synonym: Genial foramen.

 

Lingual Plate

Thin lamella of bone that constitutes the wall of the alveoli towards the tongue.

 

Mandibular Foramen

Foramen present on the medial surface of the mandible, just superior to half the height of the ramus. It constitutes the entrance to the mandibular canal for the inferior alveolar vessels and nerve.

 

Mandibular Incisure

Concavity in the superior border of the ramus of the mandible. It is bounded anteriorly by the coronoid process and posteriorly by the condylar process.

 

Mandibular Lingula

Thin triangular spine that arises anteromedial to the mandibular foramen and extends posterosuperiorly to overlap the foramen itself. The lingula gives attachment to the sphenomandibular ligament.

 

Mental Foramen

Foramen on the external surface of the mandibular body, located at half of its height. It can be located below the second premolar tooth or the space between the premolar teeth. The mental foramen is the exit point of the mental branches of the anterior inferior alveolar vessels and nerve.

 

Mental Protuberance

Triangular protuberance, with a centrally depressed base, which is enclosed between the two protuberances originated from the bifurcation of the median ridge of the body of the mandible.

 

Mental Spine

Small elevation on the posterior surface of the body of the mandible, near the posterior aspect of the symphysis menti, located superior to the anterior end of the mylohyoid line. It is divided into superior and inferior parts, which sometimes are fused. The genioglossus muscle attaches to the superior one, while the geniohyoid muscle inserts on the lower one. In some cases the spine can be absent. Synonym: Genial tubercle.

 

Mental Tubercle

Prominence located on both sides of the depression in the base of the mental protuberance.

 

Mylohyoid Groove

Groove extending anteroinferiorly from the ramus of the mandible to the area below the posterior part of the mylohyoid line. It contains the mylohyoid vessels and nerve.

 

Mylohyoid Line

Smooth ridge that divides the internal surface of the mandible bone. It gives insertion to the mylohyoid muscle, extending antero-inferiorly from the mental symphysis to a point just posterior to the third molar tooth, approximately 1 cm below the upper border of the body. It is well defined posteriorly, while progressively fades directing anteriorly.

 

Pterygoid Fovea

Small depression that gives insertion to the lateral pterygoid muscle. It is located anteriorly on the neck of the condylar process, inferior to the condyle articular surface.

 

Retromolar Fossa

The fossa located on the anterior border of the ramus of the mandible, behind the third molar tooth. It is comprised between the external oblique line and the temporal crest.

 

Sublingual Fossa

Small depression located above the mylohyoid line. It widens anteriorly in a triangular fashion and houses the sublingual gland.

 

Submandibular Fossa

Slightly concave depression located below the mylohyoid line that houses the submandibular gland.

 

Symphysis Menti

An inconstant median ridge on the external surface of the mandible bone. It  corresponds to the fused symphysis menti.

 

Temporal Crest

Ridge that descends on the medial side of the coronoid process of the mandible from its tip to the bone posterior to the third molar tooth.

 

Torus Mandibularis

Rounded prominence that is sometimes present on the medial surface of the body of the mandible, above the mylohyoid line, at the level of the molar roots.

 

Maxillary Bone

The maxillary bone is the second bone of the splanchnocranium in size. It forms part of the floor of the orbit and of the floor and lateral wall of the nasal cavity. It also contributes to defining infratemporal and pterygopalatine fossae, constituting the anterior border of the inferior orbital and pterygomaxillary fissures. Each maxilla has a body, which is approximately pyramidal, and has anterior, infratemporal (posterior), orbital, and nasal surfaces that enclose the maxillary sinus. Four processes, namely the zygomatic, frontal, alveolar, and palatine processes, arise from the maxillary body. It articulates with the frontal, ethmoid, palatine, nasal, lacrimal, zygomatic, vomer, inferior concha, and contralateral maxillary bones.

 

Full Description

 
PARTS
Anterior surface

It is more prominent inferiorly where it overlies the roots of the teeth as alveolar process. The incisive fossa is present superior to the incisor teeth, and the canine fossa lateral to it, being separated by the canine eminence. The infraorbital foramen can be located below the infraorbital margin. The medial border of the surface presents the nasal notch and half of the anterior nasal spine.

Infratemporal surface

It constitutes the concave anterior surface of the infratemporal fossa. It is separated from the anterior surface by the zygomatic process and the zygomatico-maxillary ridge (or jugal crest). It presents two or three alveolar canals and the maxillary tuberosity. It also constitutes the anterior boundary of the pterygopalatine fossa, furrowed by the groove for the maxillary nerve.

Nasal surface

It constitutes part of the inferior nasal meatus inferiorly and displays the maxillary hiatus superiorly, which allows the maxillary sinus to drain into the middle nasal meatus. Part of the superior border of the hiatus completes some of the ethmoidal air cells. The pyramid shaped maxillary sinus is the biggest of the paranasal sinuses. Its floor is related to the dental roots, and bone dehiscences are not rare. The roof of the sinus contains the infraorbital canal, which also may present bone defects. The lateral apex of the sinus extends into the zygomatic process. The walls of the sinus may present ridges anteriorly or posteriorly according to the protrusion of either the canalis sinuosus or the posterior alveolar canals, respectively. Incomplete or complete septa can be present inside the sinus. The maxillary sinus is the first to begin its development. It extends lateral to the infraorbital canal at approximately 4 years of age. The posterior part of the nasal surface is rough, where it articulates with the perpendicular plate of the palatine bone, and shows a groove that completes the greater palatine canal. The anterior part is marked by the nasolacrimal groove and, more anteriorly, by the conchal crest.

Orbital surface

It is triangular, smooth, and forms most of the floor of the orbit. It also forms the anterior edge of the inferior orbital fissure. The anterior border of the orbital surface constitutes part of the infraorbital margin, and it is continuous with the lacrimal crest of the frontal process of the maxillary bone. The lacrimal notch is present on the anteromedial aspect of the surface, where the depression indicating the origin of the inferior oblique muscle may also be visible. The infraorbital groove furrows the posterior border and continues as the infraorbital canal. The canalis sinuosus is also present within the orbital surface and continues into the anterior surface, reaching the nasal cavity.

Alveolar process

It is thick, arched, and located below the maxillary sinuses. It surrounds the palatine process anteriorly and laterally. It displays the buccal and the palatal plates, as well as interdental and inter-radicular septa.

Frontal process

It is directed posterosuperiorly and presents the anterior lacrimal crest on its lateral surface. The lacrimal tubercle is present at the junction with the orbital surface. A grooves behind the lacrimal crest completes the corresponding one on the lacrimal bone to form the lacrimal sac fossa. The medial surface is part of the lateral nasal wall and presents the ethmoidal crest. Its subapical part, superior to the ethmoidal crest, may complete some of the ethmoidal air cells. The agger nasi is located anterior to the ethmoidal crest.

Palatine process

It is thick, horizontal, and extends medially to join the contralateral palatine process with a raised medial border, which constitutes the so called nasal crest for the articulation with the vomer bone, to form the floor of the nasal cavities and the mouth roof. The palate is arched in the anteroposterior and the transverse directions, with a concave inferior surface, which shows depressions for palatine glands, vascular foramina, the grooves for the greater palatine neurovascular bundles, and the median incisive foramen. The incisive foramen is formed by two notches on the two maxillary bones, whose lateral walls are pierced by the lateral incisive foramina. These foramina communicates with the nasal cavities through the incisive canals. The inferior surface displays the incisive suture and the median palatine suture, which is usually flat, although it may arise as palatine torus. The superior surface has a raised medial edge, called the nasal crest, forming a groove, together with the contralateral one, to house the inferior border of the vomer bone. The higher anterior end of the nasal crest is called the incisor crest and joins the contralateral one to from the anterior nasal spine.

Zygomatic process

It is a pyramidal process at the convergence of the infratemporal and the orbital surfaces. It is concave posteriorly, being in continuity with the infratemporal surface. The superolateral surface is rough, due to the articulation with the zygomatic bone. Inferiorly, the zygomatico-maxillary ridge separates the facial and the infratemporal surfaces.

ARTICULATIONS

The maxillary bone articulates with the frontal, ethmoid, palatine, nasal, lacrimal, zygomatic, vomer, inferior concha, and contralateral maxillary bones.

SKELETAL LANDMARKS

The medial border and part of the inferior border of the orbit are constituted of the maxillary bone. The infraorbital foramen can be palpated 0.5-1 cm inferior to the infraorbital margin, approximately in the same vertical plane to the supraorbital and the mental foramina. 

Anatomical Details

Agger Nasi

The protuberance located anterior to the insertion of the middle nasal concha on the lateral nasal wall, at the base of the ethmoidal crest.

 

Alveolar Canals

Two or three canals visible on the infratemporal surface of the maxillary bone. They transmit the posterior superior alveolar vessels and nerves.

 

Alveolar Process

The inferior part of the maxillary bone, located below the maxillary sinuses and enclosing the palatine process. It contains the alveoli for the superior teeth.

 

Alveolus

Cavity in the alveolar process that houses a tooth. 16 alveoli for the superior teeth are present in total.

 

Anterior Lacrimal Crest

Vertical ridge that divides the lateral surface of the frontal process of the maxillary bone. It continues inferiorly into the infraorbital margin and gives attachment to the medial palpebral ligament.

 

Anterior Nasal Spine

Pointed process at the inferior end of the nasal notch. It articulates with the contralateral one forming the inferior edge of the pyriform aperture.

 

Buccal Plate

Thin lamella of bone that constitutes the wall of the alveoli towards the vestibule of the mouth.

 

Canalis Sinuosus Opening

The opening of the canalis sinuosus, which opens anterior to the incisive canal, near the nasal septum. This canal descends in the orbital floor lateral to the infraorbital canal and passes below the infraorbital foramen, after a medial turn inside the anterior wall of the maxillary sinus. Then, it reaches the anterior end of the inferior concha and follows the pyriform aperture until its exit point. This canal houses the anterior superior alveolar nerve and vessels.

 

Canine Eminence

Rounded eminence that corresponds to the alveolus of the canine tooth. It separates the incisive and canine fossae.

 

Canine Fossa

Fossa above the alveoli posterior to the canine eminence.

 

Conchal Crest

Posterosuperiorly inclined ridge for the articulation with the inferior nasal concha.

 

Ethmoidal Crest

Oblique crest located below the areas that complete the walls of ethmoidal air spaces. It articulates posteriorly with the middle nasal concha, contributing to form the axilla (i.e. curved insertion on the lateral nasal wall) of the middle turbinate.

 

Frontal Process

The process arising superiorly from the body of the mandible to articulate with the frontal bone and constitute part of the medial orbital wall and of the pyriform aperture.

 

Greater Palatine Groove

The groove posterior to the maxillary hiatus on the nasal surface. It descends antero-inferiorly from the midpoint of the posterior border of the maxillary bone. The perpendicular plate of the palatine bone completes it to form the greater palatine canal.

 

Incisive Canal

The canal lying near the median margin of the anterior part of the superior surface of the palatine process, connecting the nasal cavity and the mouth. This canal bears terminal branches of the greater palatine vessels and the nasopalatine nerve.

 

Incisive Foramen

The incisive foramen is formed by the apposition of two notches on the medial surface of the palatine processes. It lies behind the medial incisor teeth on the inferior surface.

 

Incisive Fossa

Fossa above the alveoli of the incisors, anterior to the canine eminence.

 

Incisive Notch

The notch located behind the medial incisor teeth on the inferior surface of the palatine process. It joins the contralateral one to form the incisive foramen.

 

Incisive Suture

The fused suture, more faint in elder skulls, extending from the incisive foramen to the interdental space between the lateral incisor and the canine teeth.

 

Incisor Crest

Thin ridge projecting superiorly from the raised medial border of the palatine process. It is the posterior prolongation of the nasal spine.

 

Infraorbital Canal

The anterior continuation of the infraorbital groove inside the roof and the anterior wall of the maxillary sinus. It opens on the anterior surface below the infraorbital margin transmitting the infraorbital neurovascular bundle.

 

Infraorbital Foramen

The foramen lying above the canine fossa as the opening of the infraorbital canal.

 

Infraorbital Groove

The impression of the infraorbital neuromuscular bundle on the orbital surface of the maxillary bone.

 

Infraorbital Margin

The anterior edge of the floor of the orbit, between the orbital and the anterior surfaces of the maxillary bone. It continues on the frontal process as the anterior lacrimal crest.

 

Inter-dental Septum

Lamella of bone that separates two alveoli, connecting the buccal and the palatal plates.

 

Inter-radicular Septum

Lamella of bone that separates the roots of the tooth in each alveolus. The number of septa in each alveolus changes according to the number of roots of its tooth. The incisive, canine and second premolar teeth usually have one root, the first premolars show two roots, and the molars usually three roots.

 

Lacrimal Notch

The impression for the nasolacrimal duct in the anteromedial angle of the orbital surface.

 

Lacrimal Sac Groove

Vertical groove behind the lacrimal crest that is completed by a groove on the lacrimal bone to complete the lacrimal sac fossa.

 

Lacrimal Tubercle

A small tubercle arising at the junction between the anterior lacrimal crest and the orbital surface. It can be used as a guide to the lacrimal sac.

 

Lateral Incisive Foramen

The foramen in the lateral walls of the incisive fossa through which the incisive canal reaches the mouth cavity. Sometimes anterior and posterior median incisive foramina are present, the anterior being traversed by the left nasopalatine nerve, while the posterior by the right one.

 

Maxillary Hiatus

Irregular opening that gives access to the maxillary sinus. Parts of the upper border of the hiatus complete air spaces owing to the articulations with ethmoid and lacrimal bones.

 

Maxillary Nerve Groove

Groove located on the posterolateral surface of the maxillary bone, which constitutes the smooth anterior boundary of the pterygopalatine fossa, above the maxillary tuberosity. It is the impression of the maxillary nerve on the bone.

 

Maxillary Tuberosity

A rounded eminence, that is present on the posteroinferior aspect of the body of the maxillary bone. It is rough on its lateral side where it articulates with the pyramidal process of the palatine bone.

 

Nasal Notch

The concave shaped medial edge of the anterior surface of the maxillary bone. It forms the lateral and half of the inferior borders of the pyriform aperture.

 

Naso-lacrimal Groove

The groove anterior to the maxillary hiatus that continues superiorly with the lacrimal sac groove and accounts for about 2/3 of the circumference of the nasolacrimal canal. The descending part of the lacrimal bone and the lacrimal process of the inferior nasal concha complete the rest of the canal; which allows the nasolacrimal duct to open into the inferior meatus.

 

Palatal Plate

Thin lamella of bone that constitutes the wall of the alveoli towards the palatine process of the maxillary bone.

 

Palatine Gland Depression

Depressions and foramina for the palatine glands marks the inferior surface of the palatine process.

 

Palatine Grooves

Sulci on the inferior surface of the palatine process housing branches of the greater palatine neurovascular bundle, and constituting the anterior extension of those present on the palatine bone.

 

Palatine Process

The part of the maxillary bone that extends medially and joins the contralateral one to form the floor of the nasal cavities and the mouth roof. It has a raised medial border, which constitutes the nasal crest for the articulation with the vomer bone.

 

Zygomatico-Maxillary Ridge

The crest that ascends from the alveolus of the first molar tooth to the zygomatic process and contributes to the separation between the anterior and the infratemporal surfaces. Synonym: Jugal crest.

 

Zygomatic Process

The process that projects laterally from the body of the maxillary bone to articulate with the zygomatic bone.

 

Nasal Bone

The nasal bone, small and variable in size and shape, forms part the nasal bridge. It has two surfaces and four borders, and articulates with the frontal, ethmoid, maxillary, and contralateral nasal bones.

 

Full Description

ARTICULATIONS

The nasal bone articulates with the frontal, ethmoid, maxillary, and contralateral nasal bones.

Anatomical Details

Anterior Ethmoidal Nerve Groove

Longitudinal groove on the internal surface of the nasal bone lodging the anterior ethmoidal nerve.

 

Venous Anastomosis Foramen

Small foramen located almost centrally in the nasal bone transmitting a small vein.

 

Occipital Bone

The occipital bone forms most of the posterior cranial fossa and of the cranial base. It is approximately trapezoid and is pierced by the foramen magnum. It is composed of the four following parts: the anterior quadrangular-shaped basilar (basioccipital) part, the posteriorly expanded squamous part, and two lateral condylar parts. It articulates with the temporal, sphenoid, and parietal bones.

 

Full Description

 
PARTS
Basilar part

It extends anterosuperiorly from the foramen magnum, reaching the body of the sphenoid bone. In a young skull, the spheno-occipital synchondrosis is present, as it ossifies by the age of 25. The inferior surface shows two small depressions, or sometimes tubercles, anterior to the occipital condyle, where the anterior rectus capitis inserts. The inferior surface displays also the pharyngeal tubercle. Approximately 1 cm behind it, the anterior atlanto-occipital membrane inserts on the anterior border of the foramen magnum. The superior surface shows a concavity facing posterosuperiorly, which slopes forward and upward from the foramen magnum. It joins the body of the sphenoid to form the lower 2/3 of the clivus; while the dorsum sellae constitutes its upper 1/3.

Lateral (condylar) parts

The two parts surrounding the foramen magnum laterally. Each part displays the occipital condyle and the condylar fossa behind it. The tubercle for the alar ligament is present on the medial aspect of the condyle, whereas the hypoglossal (or anterior condylar) canal is present superior to the occipital condyle, with its medial end located below the jugular tubercle. The posterior condylar canal pierces the condylar fossa and reaches the sulcus for the sigmoid sinus on the internal surface. Nevertheless, it can be absent or formed by multiple smaller canals. From the posterior part of each condyle, the jugular process projects laterally, to articulate with the petrous part of the temporal bone. In the young, this part is separated from the temporal bone by cartilage, which begins to ossify by the age of 25. The anterior edge of the jugular process forms the posterior boundary of the jugular foramen, which houses anteroposteriorly: the inferior petrosal sinus; the glossopharyngeal, vagus and accessory cranial nerves; and the internal jugular vein. The jugular process is marked by an indentation, called the jugular notch, which may be partially subdivided by a small intrajugular process. The jugular notch constitutes the inferior ending of the sulcus for the sigmoid sinus. A paramastoid process can project inferiorly from the jugular process, and it may even articulate with the transverse process of the atlas.

Squamous part

The external surface shows the median external occipital protuberance and crest. The highest, superior, and inferior nuchal lines are visible lateral to them on both sides. The internal surface shows the sulcus for the superior sagittal sinus, the torcular, the internal occipital protuberance, and the internal occipital crest in the midsagittal plane. The sulci for the transverse sinuses arise from the internal occipital protuberance and run laterally and then anteriorly towards the sulci for the sigmoid sinuses. Four fossae are defined by these sagittal and transverse bony landmarks: the superior two house the occipital poles, while the inferior two accommodate the cerebellar hemispheres. The upper border of the squamous part may present a variable number of sutural bone included in the lambdoid suture. A large median sutural bone, called the interparietal bone, the Inca bone, or the ossicle of Goethe, is sometimes present.

ARTICULATIONS

The occipital bone articulates with the temporal, sphenoid, and parietal bones.

SKELETAL LANDMARKS

The external occipital protuberance, more prominent in males, can be palpated in the median plane and indicates the confluence of dural sinuses on the other side of the bone and the medial end of the two superior nuchal lines. These lines can be followed laterally until their lateral ends, which are located posterior to the convexity of the mastoid processes.

Anatomical Details

Alar Ligament Tubercle

Small tubercle located on the roughened medial aspect of the occipital condyles giving attachment to the alar ligament.

 

Cerebellar Hemisphere Fossa

Quadrilateral fossa derived from the division of the internal surface of the occipital bone by the internal occipital protuberance and axial and sagittal ridges of the squama. Of the four fossae created by them, the two inferior fossae are adapted to the cerebellar hemispheres.

 

Condylar Fossa

The area behind the occipital condyle that harbors the posterior margin of the superior articular facet of the atlas when the head is fully extended.

 

Condyle Articular Surface

The part of the condyle surface facing the articular facet of the atlas. It is convex and infers-laterally directed.

 

Clivus

The part of the skull base located anterior to the foramen magnum and posteroinferior to the pituitary fossa. It slopes anterosuperiorly and is completed owing to the articulation of the occipital bone with the sphenoid bone. Its upper 1/3 consists in the dorsum sellae, while the lower 2/3 are constituted by the basilar part of the occipital bone and the part of the sphenoid body posteroinferior to the dorsum sellae.

 

External Occipital Crest

Vertical crest located midsagittally on the external surface of the occipital bone. It extends from the external occipital protuberance to the foramen magnum, and it can be clearly visible or faint.

 

External Occipital Protuberance

The midsagittal elevation on the external surface of the occipital bone, located midway between the lambdoid suture and the foramen magnum.

 

Foramen Magnum

The foramen located between the basilar, condylar, and squamous parts of the occipital bone. It has an oval shape, with an anteroposterior long axis, and it is wider posteriorly. It contains the lower end of the medulla oblongata, the vertebral arteries and the spinal accessory nerves. It is also crossed by the apical ligament of the dens and the tectorial membrane reaching the internal surface of the occipital bone.

 

Highest Nuchal Line

The horizontal ridge extending laterally from the external occipital protuberance. Its medial part gives insertion to the galea aponeurotica, while its lateral one gives attachment to the occipital part of occipitofrontalis muscle.

 

Hypoglossal Canal

The anterolaterally directed canal located superior to the condyle, with the internal end above the anterolateral part of the foramen magnum. It can be partly or entirely divided by a spicule of bone. It houses the hypoglossal nerve, accompanied by a meningeal branch of the ascending pharyngeal artery and an emissary vein from the basilar plexus. Synonym: Anterior condylar canal.

 

Inferior Nuchal Line

Horizontal line extending laterally from the midpoint of the external occipital crest on each side. The lateral part of the inferior nuchal line and the bone immediately below give attachment to the posterior rectus capitis major, while its medial part and the bone between it and the foramen magnum give insertion to the posterior rectus capitis minor. The area between the superior and the inferior nuchal lines gives attachment to semispinalis capitis muscle on its medial portion and to superior obliquus capitis on its lateral portion.

 

Internal Occipital Crest

Vertical crest descending from the internal occipital protuberance and bifurcating behind the foramen magnum. It gives attachment to the falx cerebelli and underlies the occipital sinus.

 

Internal Occipital Protuberance

The midsagittal elevation on the internal surface of the squama of the occipital bone. It is located at the confluence of the transverse sinuses sulci, the internal occipital crest, and the sagittal sinus sulcus.

 

Jugular Notch

Small indentation on the jugular process of the jugular part of the occipital bone.

 

Jugular Process

A quadrangular-shaped plate that projects laterally from the posterior half of the condyle and articulates with the petrous part of the temporal bone. It contributes to the formation of the posterior edge of the jugular foramen with its anterior free border. Its inferior surface gives insertion to the lateral rectus capitis muscle.
The jugular foramen houses anteroposteriorly the inferior petrosal sinus; the glossopharyngeal, vagus and accessory cranial nerves; and the internal jugular vein.

 

Jugular Tubercle

An oval process located on the superior surface of the lateral part of the occipital bone, above the medial end of the hypoglossal canal.

 

Occipital Condyle

Oval-shaped or reniform process projecting inferiorly anterolateral to the foramen magnum. It bears an articular facet and its anterior margin overlaps the anterior edge of the foramen magnum. The bilateral long axes converge anteromedially. The condyle is sometimes divided into two parts, and the number of articular facets of the atlas varies accordingly.

 

Occipital Lobe Fossa

Triangular fossa derived from the division of the internal surface of the occipital bone by the internal occipital protuberance and axial and sagittal ridges of the squama. Of the four fossae created by them, the two superior fossae are adapted to the poles of the occipital lobes.

 

Pharyngeal Tubercle

Prominence located midsagittally on the inferior surface of the basilar part of the occipital bone. It is approximately 1 cm anterior to the foramen magnum, and gives attachment to the fibrous pharyngeal raphe and to the longus capitis muscle.

 

Posterior Condylar Canal

The canal perforating the roof of the condylar fossa allowing the exit of a sigmoid emissary vein. It is sometimes absent and can have variations being a single canal or multiple smaller canals.

 

Sigmoid Sinus Sulcus

The sulcus underlying the sigmoid sinus that curves antero-medially around a hook-shaped process of the jugular process to end at the jugular notch.

 

Superior Nuchal Line

A horizontal ridge that extends laterally from the external occipital protuberance on each side. Its medial third and the external occipital protuberance give insertion to the trapezius muscle, while its lateral third gives insertion to the splenius capitis. The lateral half of the line gives insertion to the sternocleidomastoid muscle. The area between the superior and the inferior nuchal lines gives attachment to semispinalis capitis muscle on its medial portion and to superior obliquus capitis on its lateral portion.

 

Superior Sagittal Sinus Sulcus

A wide sulcus with raised edges that reaches the frontal crest on the frontal bone, continues for the entire length of the parietal bones (with half of the sulcus on both parietal bones), and extends from the lambdoid suture to the internal occipital protuberance on the occipital bone. Its edges give attachment to the falx cerebri.

 

Torcular

Impression on the internal occipital protuberance, indicating the position of the confluence of the sinuses. It is on the side of the transverse sinus whose sulcus is the continuation of the superior sagittal sinus sulcus, usually the right one. The other transverse sinus receives the straight sinus.

 

Transverse Sinus Sulcus

The sulci for the transverse sinuses that reach the lateral angles of the squamous part on each side, directing laterally from the internal occipital protuberance. Their margins give attachment to the tentorium cerebelli.

 

Palatine Bone

The palatine bone is L-shaped, contributing to the floor and lateral walls of the nose, to the floor of the orbit, and the floor of the hard palate. It constitutes the medial wall of the pterygopalatine fossa, and contributes to the pterygoid fossa with its pyramidal process. It is composed of two plates (horizontal and perpendicular) and of three processes (pyramidal, orbital, and sphenoidal). It articulates with the maxillary, inferior concha, ethmoid, sphenoid, vomer, and contralateral palatine bones.

 

Full Description

 
PARTS
Horizontal plate

The quadrangular process, with a concave and thin posterior border, forming the posterior quarter of the hard palate. The posterior edge joins the contralateral one to form the posterior nasal spine. The medial border projects superiorly forming the posterior part of the nasal crest, which is completed by the contralateral horizontal plate. Its inferior surface shows the greater palatine foramen and the palatine crest, which extends medially from behind the foramen. The palatine sulci are visible arising from the greater palatine foramen.

Perpendicular plate

The ethmoidal and conchal crests are visible on the nasal surface, and define the portions of the perpendicular plate contributing to the inferior, middle, and superior nasal meatuses. The maxillary surface is rough where it articulates with the maxillary bone; on the contrary, it is smooth anteriorly, where the maxillary process overlaps with the maxillary hiatus forming part of the medial wall of the maxillary sinus. The posterosuperior part of the maxillary surface constitutes also the medial wall of the pterygopalatine fossa. The greater palatine groove is present on the maxillary surface. In some cases, the greater palatine canal is formed by the palatine bone only. The superior border shows the orbital process, the sphenoidal process, and the sphenopalatine notch between them. The pyramidal process is in continuity with the posterior and the inferior borders. The inferior border presents the lower end of the greater palatine groove.

Orbital Process

A superolaterally directed process arising from the anterior border of the perpendicular plate. It contributes to the orbit between the maxillary and the ethmoidal bones, and shows an air sinus completed by the sphenoidal concha. It also constitutes the medial part of the inferior edge of the inferior orbital fissure, and may present a groove in continuity with the maxillary nerve groove on the maxillary bone.

Pyramidal process

A posteroinferiorly directed process arising at the junction between the perpendicular and the horizontal plates. It occupies the space between the maxillary bone and the pterygoid process.
The lesser palatine foramina are present on its inferior surface and communicates with the greater palatine groove.

Sphenoidal process

Thin, posterosuperiorly directed process, arising from the posterior border of the perpendicular plate. A groove contributing to the formation of the palatovaginal canal is present on its superior surface. The vaginal process of the sphenoid bone, which articulates with the posterior border of the sphenoidal process, completes the palatovaginal canal. The inferomedial surface constitutes part of the roof and the lateral wall of the nasal cavity, with its medial border articulating with the vomer, while the lateral surface articulates with the medial pterygoid plate posteriorly.

ARTICULATIONS

The palatine bone articulates with the maxillary, inferior concha, ethmoid, sphenoid, vomer, and contralateral palatine bones.

Anatomical Details

Conchal Crest

The ridge projecting from the medial surface of the palatine bone to articulate with the inferior nasal concha.

 

Ethmoidal Crest

The ridge projecting from the medial surface of the palatine bone to articulate with the middle nasal concha.

 

Greater Palatine Canal

The inferior prolongation of the greater palatine groove in cases where the neurovascular bundle traverses the palatine bone.

 

Greater Palatine Foramen

The foramen that lies behind the transverse palatine suture, near its lateral end. It is the exit point of the grater palatine neurovascular bundle that reaches the mouth cavity.

 

Greater Palatine Groove

A deep, anteroinferiorly descending groove lying on the maxillary surface to transmit the greater palatine vessels and nerve. It is converted into a canal by the maxillary bone to form the greater palatine canal.

 

Horizontal Plate

The horizontal, medially directed quadrangular process that constitutes the posterior nasal floor, being transversely concave. It forms also the posterior quarter of the bony palate.

 

Lesser Palatine Foramen

The small foramina, usually two, that are present on the inferior surface of the pyramidal process, behind the greater palatine foramen. They transmit the lesser palatine nerves and vessels.

 

Maxillary Process

A pointed lamina arising anteriorly at the level of the conchal crest, projecting inferoposterior to the maxillary process of the inferior concha, and forming part of the medial wall of the maxillary sinus.

 

Orbital Process

Superolaterally directed process arising from the anterior border of perpendicular plate with a constricted neck. It reaches the orbit between the ethmoid and the sphenoid bones, contributing to form part of its medial wall and of the medial wall of the pterygopalatine fossa.

 

Palatine Air Sinus

The opening of an air sinus on the posterior (sphenoidal) surface of the orbital process. It is completed by the sphenoidal concha and, usually, communicates with the sphenoidal sinus. Sometimes, it communicates with the posterior ethmoidal air cells, while rarely it opens towards both the ethmoidal air cells and the sphenoid sinus.

 

Palatine Crest

A curved ridge that is often present on the inferior surface of the horizontal plate, extending from behind the greater palatine foramen towards the posterior nasal spine.

 

Palatine Grooves

Sulci on the inferior surface of the horizontal plate housing branches of the greater palatine neurovascular bundle from the greater palatine foramen.

 

Palatovaginal Canal

A groove that contributes to the formation of the palatovaginal canal that is visible on the superior surface of the sphenoidal process.

 

Perpendicular Plate

The thin perpendicular plate contributes to the inferior, middle and superior meatuses. Its medial surface is concave where it contributes to the inferior meatus. A shallow depression comprised between the ethmoidal and the conchal crests forms part of the middle meatus. A horizontal groove, superior to the ethmoidal crest, forms part of the superior meatus.

 

Posterior Nasal Spine

The posterior midsagittal projection of the horizontal plate that joins the contralateral one forming the posterior nasal spine.

 

Pyramidal Process

Posterolaterally sloping process arising from the junction between the horizontal and perpendicular plates reaching the angular space between the pterygoid plates of the sphenoid bone, where it completes the lower part of the pterygoid fossa. This area gives attachment to the fibers of the superficial head of medial pterygoid muscle. A smooth triangular part of the process appears in the infratemporal fossa between the lateral pterygoid plate and the maxillary tuberosity.

 

Sphenoidal Process

A thin plate, smaller than the orbital process, which is directed superomedially contributing to the roof of the nasal cavity and to part of the medial wall of the pterygopalatine fossa.

 

Sphenopalatine Notch

An indentation in the superior edge of the perpendicular plate, connecting the pterygopalatine fossa and the posterior part of the superior meatus. It allows the sphenopalatine vessels and the posterior superior nasal nerves to enter the nasal cavity. The orbital and the sphenoidal processes constitute its anterior and posterior borders, respectively.

 

Parietal Bone

The parietal bone forms part of the roof of the cranium. It is irregularly quadrilateral shaped, with two surfaces, four angles, and four borders. It articulates with the frontal, sphenoid, temporal, occipital, and contralateral parietal bones.

 

Full Description

ARTICULATIONS

The parietal bone articulates with the frontal, sphenoid, temporal, occipital and contralateral parietal bones.

Anatomical Details

Inferior Temporal Line

Ridge that traverses the external surface of the parietal bone and is more evident posteriorly, where it becomes the supramastoid crest. It gives insertion to the temporal muscle.

 

Middle Meningeal Frontal Branch Groove

The impression of the frontal branch of the middle meningeal artery on the internal surface.

 

Middle Meningeal Parietal Branch Groove

The impression of the parietal branch of the middle meningeal artery on the internal surface.

 

Parietal Foramen

An inconstant foramen that can be found near the superior border and 3,5 cm anterior to lambda. It houses a venous anastomosis between the superior sagittal sinus and the extracranial circulation. Sometimes, it is also traversed by a branch of the occipital artery.

 

Parietal Tuberosity

The convexity of the external surface of the parietal bone.

 

Superior Sagittal Sinus Sulcus

A wide sulcus with raised edges that reaches the frontal crest on the frontal bone, continues for the entire length of the parietal bones (with half of the sulcus on both parietal bones), and extends from the lambdoid suture to the internal occipital protuberance on the occipital bone. Its edges give attachment to the falx cerebri.

 

Superior Temporal Line

Ridge that traverses the external surface of the parietal bone and tends to fade posteriorly. Its gives insertion to the temporal fascia.

 

Vertex

The uppermost point of the skull.

 

Sphenoid Bone

The sphenoid bone is located in the middle of the skull base, between the frontal, ethmoidal, occipital, and temporal bones. It has a butterfly-like shape, with a central body, and greater and lesser wings spreading laterally from the body on both sides. In addition, it shows two inferiorly directed pterygoid processes arising at the junction between the body and the greater wings. The sphenoid bone contributes to the lateral and superior walls of the orbit, to the floor and lateral walls of the skull, to the roof of the rhinopharynx, and to the posterior wall of the nasal cavities. Moreover, it constitutes the posterior wall of the pterygopalatine fossa and the medial wall of the infratemporal fossa. The body of the sphenoid is pneumatized, containing the sphenoid sinuses. It articulates with the ethmoid, frontal, parietal, zygomatic, temporal, occipital, vomer, and palatine bones.

 

Full Description

 
PARTS
Body

It is roughly cuboid shaped and contains two sphenoid sinuses, separated by the intersinusal septum. Its superior surface constitutes the planum, or jugum, sphenoidale, which is bound posteriorly by the prechiasmatic sulcus. The optic canals are located lateral to the prechiasmatic sulcus, and the tuberculum sellae can be seen posterior to it. The variably prominent middle clinoid processes may be visible lateral to the tuberculum. The pituitary fossa is bound anteriorly by the tuberculum sellae and posteriorly by the dorsum sellae, contributing to the formation of the sella turcica on the superior surface of the body. The pituitary fossa does not present lateral walls and it is in continuity with the carotid sulci and the superior surfaces of the greater wings, lateral to the sulci. The posterior clinoid processes are present on the superolateral part of the dorsum sellae, while the petrosal processes are located below the dorsum sellae. The lateral edge of each carotid sulcus is constituted of the lingula. The anterior surface of the body is marked by the sphenoidal crest, which is located between the sphenoidal conchae. The conchae are divided into anterior and posterior parts, and surround the ostia of the sphenoid sinuses. The inferior surface of the body presents the sphenoid rostrum, bound laterally by the progressively diverging edges of the sphenoidal crest. The thin vaginal processes are present medial to the pterygoid processes.

Greater wings

Two processes arising from the body and contributing to the skull base and the lateral wall of the skull. The triangular posterior edge of the wing wedges between the petrous and the squamous parts of the temporal bone, constitutes the anterior limit of the medial half of the foramen lacerum, and presents the posterior opening of the Vidian, or pterygoid, canal. The foramina ovale, rotundum, and spinosum are visible on the superior surface, piercing both of the greater wings. The foramina ovale and spinosum are seldom confluent. The sphenoid emissary foramen (of Vesalius) may be present medial to the foramen ovale in approximately 40% of people, and connect the cavernous sinus with the pterygoid venous plexus. The lateral surface of the greater wing is marked by the infratemporal crest, that reaches the anterior aspect of the lateral pterygoid plate.
The inferior surface is pierced by the foramina ovale and spinosum, while the foramen rotundum opens on the anterior surface below the medial end of the superior orbital fissure. The sphenoid spine projects inferiorly from behind the foramen spinosum, and is marked medially by the groove for the chorda tympani. The sulcus tubae is present near the sphenoid spine. Lateral to the sphenoid spine, the rough surface for the articulation with the squamous part of the temporal bone faces internally, while in the part of the greater wing contributing to the lateral wall of the skull it faces externally. The superior edge of the greater wing has a rough triangular area on the internal surface for the articulation with the frontal bone, which continues medially as the inferior margin of the superior orbital fissure. Its anterior angle and the anterior edge of the greater wing articulate with the zygomatic bone. The orbital surface is located between the anterior edge of the greater wing and the inferior margin of the superior orbital fissure. The foramen of Hyrtl piercing the orbital surface may be observed. The inferior border of the orbital surface bounds the inferior orbital fissure posterolaterally.

The internal surface of the greater wing is grooved by the impression of the frontal branch of the middle meningeal artery.

Lesser wings

Two triangular bone projections arising from the body and directed laterally. They separate the anterior and the middle cranial fossae, projecting posteriorly towards the lateral fissures of the cerebral hemispheres. The posterior edge of the lesser wing continues medially into the anterior clinoid process, which may join the middle clinoid process to form the carotico-clinoid foramen. The anterior clinoid process shows also two insertions on the body of the sphenoid: a superior thin root, above the optic canal; and an inferior thick root, namely the optic strut, found below the optic canal.

Pterygoid processes

They arise from the junction between the greater wings and the body of the sphenoid, and direct inferiorly. Each process shows the medial and the lateral pterygoid plates, which are separated by the pterygoid fossa. The superior parts of the medial and the lateral plates are fused anteriorly, while their inferior parts diverge, constituting the pterygoid fissure. The posterior edge of the medial plate presents the processus tubarius at its midpoint, the pterygoid tubercle at its upper end, and the pterygoid hamulus at its lower end. The medial plate splits superiorly to enclose the scaphoid fossa. The vaginal process is located medial to the medial pterygoid plate, and contributes to the palatovaginal canal, articulating with the sphenoidal process of the palatine bone. It further articulates with the ala of the vomer, contributing to the vomerovaginal canal. The anterior surface of the root of the pterygoid process is pierced by the anterior opening of the Vidian, or pterygoid, canal.

Sphenoidal conchae

Curved plates arising from the inferior part of the anterior aspect of the body of the sphenoid. Each of them has an anterior vertical part completing the posterior ethmoidal sinuses, and a posterior horizontal part constituting part of the nasal roof. They are pierced by the ostium of the sphenoid sinus. The sphenoidal crest and the sphenoid rostrum are located between the conchae. The posterosuperior surface of the concha contributes to the formation of the walls of the sphenoid sinus.

Superior orbital fissure

The opening connecting the cranial cavity and the orbit. It is bound medially by the body of the sphenoid, superiorly by the lesser wing, inferiorly by the greater wing, and laterally by the frontal bone between the greater and the lesser wings.

ARTICULATIONS

The sphenoid bone articulates with the ethmoid, frontal, parietal, zygomatic, temporal, occipital, vomer, and palatine bones.

Anatomical Details

Anterior Clinoid Process

The posteriorly directed, medial prolongation of the posterior edge of the lesser wing. The anterior and middle clinoid processes are sometimes united to form a carotico-clinoid foramen.

 

Carotid Sulcus

The sulcus located above the root of the greater wing accommodating the internal carotid artery.

 

Chorda Tympani Groove

A groove on the medial side of the spine of the sphenoid. It houses the chords tympani nerve after its exit from the petro-tympanic fissure.

 

Dorsum Sellae

Approximately rectangular-shaped process posterior to the pituitary fossa. It constitutes the upper 1/3 of the clivus. The remaining 2/3 are formed by the portion of sphenoid bone posteroinferior to the dorsum sellae and by the basilar portion of the occipital bone.

 

Foramen Ovale

The foramen located anteromedial to the foramen spinosum, posterolateral to the foramen rotundum, and lateral to the foramen lacerum. It connects the middle cranial fossa and the infratemporal fossa, transmitting the mandibular nerve, the lesser petrosal nerve, the venous anastomosis between the cavernous sinus and the pterygoid venous plexus, and the accessory meningeal branch, arising from the maxillary artery. Occasionally the foramen ovale is fused with the foramen spinosum.

 

Foramen Rotundum

The most anteromedial of the three foramina of the greater wing of the sphenoid bone. It connects the middle cranial fossa and the pterygopalatine fossa, transmitting the maxillary nerve.

 

Foramen Spinosum

The smaller and rounder foramen of the greater wing of the sphenoid. It is located posterolateral to the foramen ovale, transmitting the middle meningeal artery and a recurrent meningeal branch of the mandibular nerve. Occasionally the foramen ovale is fused with the foramen spinosum, or the posterior edge of the foramen spinosum can be absent.

 

Greater Wing

Process arising from the body of the sphenoid and extending posterolaterally from the skull base to the lateral surface of the skull. Its concave internal surface is part of the middle cranial fossa. Its triangular posterior edge is located in the angle between the petrous and squamous parts of the temporal bone. Its posterior edge is the anterior limit of the medial half of the foramen lacerum.

 

Hyrtl Foramen

A foramen that can be present on the greater wing, connecting the middle cranial fossa and the orbit. It is lateral to the superior orbital fissure, below the posterior margin of the lesser wings of the sphenoid bone. It houses the meningolacrimal artery, when present, or occasionally a recurrent meningeal branch from the lacrimal artery.

 

Infratemporal Crest

Ridge that divides the lateral surface of the greater wing into temporal and infratemporal surfaces. It continues anteromedially and inferiorly towards the anterior aspect of the lateral pterygoid plate, bounding the pterygo-maxillary fissure posteriorly.

 

Lateral Pterygoid Plate

Broad and thin plate showing a slight lateral concavity and projecting posterolaterally. Its lateral surface, which forms part of the medial wall of the infratemporal fossa, gives origin to the lateral pterygoid muscle. Its medial surface forms the lateral wall of the pterygoid fossa. The upper part of its anterior border is the posterior boundary of the pterygo-maxillary fissure, while its lower part articulates with the palatine bone.

 

Lesser Wing

A triangular process arising laterally from the anterosuperior region of the body. Its separates the frontal lobe of the brain from the superior orbital fissure and the temporal lobe. Its posterior edge separates the anterior and the middle cranial fossae.

 

Lingula

The bony crest arising as the lateral edge of the carotid sulcus, and extending posteriorly over the posterior opening of the pterygoid canal.

 

Medial Pterygoid Plate

Narrower and longer plate with respect to the lateral one, with a sharp posterior edge. Its lateral surface forms the medial wall of the pterygoid fossa; while its medial surface is the lateral boundary of the posterior nasal aperture. It articulates with the posterior border of the perpendicular plate of the palatine bone in the lower part of its anterior margin. The posterior margin of the medial pterygoid plate gives insertion to the pharyngobasilar fascia. The lower end of the medial pterygoid plate gives attachment to the superior pharyngeal constrictor.

 

Middle Clinoid Process

Variably prominent process inferolateral to the tuberculum sellae and medial to the carotid sulcus. The anterior and middle clinoid processes are sometimes united to form a caroticoclinoid foramen.

 

Middle Meningeal Frontal Branch Groove

The impression of the frontal branch of the middle meningeal artery on the internal surface.

 

Optic Canal

The canal connecting the cranial cavity and the orbit containing the optic nerve and the ophthalmic artery.

 

Optic Strut

The thick triangular root posteroinferior to the optic canal. It corresponds to the lateral optico-carotid recess visible from inside the sphenoid sinus.

 

Palatovaginal Canal

The groove on the inferior surface of the vaginal process that is completed anteriorly by the sphenoidal process of the palatine bone to form the palatovaginal canal. The palatovaginal canal transmits the pharyngeal branches from the maxillary artery and the pterygopalatine ganglion.

 

Petrosal Process

The small process present below the dorsum sellae articulating with the apex of the petrous part of the temporal bone.

 

Pituitary Fossa

The fossa, contained in the sella turcica, housing the pituitary gland. It is bounded by bony walls only anteriorly and posteriorly.

 

Planum Sphenoidale

The smooth part located anteriorly on the superior surface, between the lesser wings and anterior to the prechiasmatic sulcus. Synonym: Jugum sphenoidale.

 

Posterior Clinoid Process

The process arising from the superior lateral angle of the dorsum sellae. It gives insertion to the diaphragma sellae and the tentorium cerebelli.

 

Prechiasmatic Sulcus

The sulcus extending between the optic canals and lying anterior to the tuberculum sellae. It constitutes the posterior border of the planum.

 

Processus Tubarius

The process located in the midpoint of the posterior edge of the medial pterygoid plate. It is attached to the pharyngeal end of the pharyngo-tympanic tube.

 

Pterygoid Fossa

The cuneiform fossa between the medial and the lateral pterygoid plates. The upper parts of the pterygoid plates are fused closing the fossa anteriorly. Their inferior parts are separated delineating the pterygoid fissure, which is closed anteriorly by the pyramidal process of the palatine bone. Medial pterygoid and tensor veli palatini muscles originate from the pterygoid fossa.

 

Pterygoid Hamulus

The unciform, laterally directed process arising from the inferior end of the medial pterygoid plate. It gives attachment to the pterygo-mandibular raphe, and the tendon of tensor veli palatini curves medially around it.

 

Pterygoid Tubercle

The small tubercle inferior to the posterior opening of the Vidian canal, at the upper end of the medial pterygoid plate.

 

Scaphoid Fossa

The fossa comprised between the two laminae created by the subdivision of the medial pterygoid plate in its superior portion. It gives origin to part of the tensor veli palatini muscle.

 

Sella Turcica

The superior part of the body of the sphenoid, above the sphenoid sinus, containing the pituitary gland into the pituitary fossa.

 

Sphenoidal Concha Anterior Part

Vertical quadrangular part of the concha completing the posterior ethmoidal sinuses with a superolateral depressed area. It articulates below with the orbital process of the palatine bone. It also shows a smooth and triangular inferomedial area constituting part of the nasal roof.

 

Sphenoidal Concha Posterior Part

Horizontal triangular part of the concha facing the nasal cavities, completing the sphenopalatine foramen and constituting part of the floor of the sphenoid sinus. Its medial edge forms the rostrum of the sphenoid in the midline, joining the contralateral one. Its apex is posteriorly directed and superomedial to the vaginal process. Both the posterior part of the concha and the vaginal process articulate with the ala of the vomer.

 

Sphenoidal Crest

A protrusion located where the anterior parts of the two conchae joins in the midline.

 

Sphenoidal Rostrum

The midsagittal process located where the posterior parts of the sphenoidal conchae joins, inferior to the sphenoidal crest.

 

Sphenoid Sinus Ostium

The hole that connects the sphenoid sinus with the spheno-ethmoidal recess, piercing the upper portion of the smooth area of the anterior part of the sphenoidal concha.

 

Sphenoid Spine

The spine projecting inferiorly from the greater wing posterior to the foramen spinosum. Its tip gives attachment to the spheno-mandibular ligament.

 

Sulcus Tubae

The sulcus located inferior to the posterior margin of the greater wing, containing the cartilaginous pharyngo-tympanic tube. It is completed by the sphenoid spine, laterally, and the petrous part of the temporal bone, posteromedially.

 

Superior Orbital Fissure

The approximately triangular aperture connecting the cranial cavity and the orbit. Its medial border is constituted by the body of the sphenoid. Its superior border is determined by the lesser wing, and supero-laterally, between the greater and the lesser wings, by the frontal bone. Its inferior border corresponds to the medial margin of the orbital surface of the greater wing of the sphenoid. It is traversed by: the lacrimal, frontal, and IV cranial nerves, the superior ophthalmic vein, and the recurrent meningeal branch arising from the lacrimal artery passing outside the annulus of Zinn; the nasociliary, abducent, and superior and inferior divisions of the III cranial nerves passing inside the annulus of Zinn.

 

Tuberculum Sellae

The bony elevation posterior to the prechiasmatic sulcus, comprised between the lateral tubercular crests, which reach the middle clinoid processes. It constitutes the superior border of the anterior wall of the sella turcica, and gives insertion to the diaphragma sellae.

 

Vaginal Process

Thin bony projection arising medially from the base of the medial pterygoid plate and below the posterior part of the rostrum.

 

Vidian Canal

The canal whose posterior end is located in the posteromedial margin of the greater wing, at the anterior margin of the foramen lacerum, above and between the pterygoid plates of the sphenoid bone. Its anterior end is on the posterior surface of the pterygopalatine fossa. It houses the Vidian nerve, and accompanying blood vessels. Synonym: Pterygoid canal.

 

Teeth

The adult skull shows 32 teeth. Each quadrant of the mouth has 8 teeth including the following: 1 medial and 1 lateral incisors, 1 canine, 2 premolars, and 3 molars. The third molar however may not be present. The inferior incisive, canine and premolar teeth typically have one root, whereas the three molar teeth show either two or three roots. The superior incisive, canine, and second premolar teeth typically have one root, the first premolars two roots, and the molars three roots.

 

 

Temporal Bone

The temporal bone contributes to the lateral skull base, the lateral wall of the skull, and the zygomatic arch. It consists of the four following parts: the flat, vertical squamous part, which is the largest part, showing a medial and a lateral surfaces; the posteroinferior mastoid part, which gives insertion to the muscles of the neck and has a pneumatization in communication with the middle ear; the petrous part, located between the greater wing of the sphenoid and the clivus, containing the middle and inner ears, the VII cranial nerve together with the VIII, and the internal carotid artery; and the thin plate of bone called tympanic part, which surrounds the base of the styloid process. The temporal bone articulates with the sphenoid, occipital, parietal, and zygomatic bones.

 

Full Description

 
PARTS
Mastoid part

It is the posteroinferior part of the bone and presents an anteroinferior projection, namely the mastoid process, which is larger in adult males. The mastoid foramen is present posteriorly on the lateral surface of the mastoid part. The extracranial medial surface is marked by the mastoid notch and the occipital groove. The intracranial medial surface of the mastoid part is grooved by the sulcus for the sigmoid sinus, and grooves for meningeal branches of the occipital artery may be observed near the intracranial opening of the mastoid foramen.

Petrous part

It is pyramid-shaped and wedges between the sphenoid and occipital bones. It contains the vestibular and the cochlear systems, the facial canal, and the carotid canal. It presents the anterior, posterior, and inferior surfaces that project anteromedially towards the apex, which constitutes the posterolateral border of the foramen lacerum. The anterior opening of the carotid canal pierces the apex of the petrous part. The anterior surface contributes to the floor of the middle cranial fossa, and is separated from the internal surface of the squama by remnants of the petro-squamosal suture, while the posterior surface faces the posterior cranial fossa. The trigeminal impression is located posterior to the apex, and anterior to the internal acoustic meatus and the bone overlying the cochlea. The arcuate eminence arises from the anterior surface of the petrous part. The tegmen tympani is the part of the anterior surface contained between the squama and the arcuate eminence. The foramina for the greater and lesser petrosal nerves pierce the anterior surface of the petrous part anterior to the arcuate eminence, and are in continuity with grooves for the same nerves. The posterior surface of the petrous part is pierced by the internal acoustic meatus and the vestibular canaliculus. The subarcuate fossa is visible posterior to the internal acoustic meatus, and it is pierced by the subarcuate canal. 
The superior border, located between the anterior and the posterior surfaces, gives insertion to the tentorium cerebelli, and is grooved by the superior petrosal sinus. 
The inferior surface of the petrous part gives insertion to the levator veli palatini and the cartilaginous pharyngo-tympanic tube, completing the sulcus tubae on the sphenoid bone, and it articulates with the occipital bone owing to the fibrocartilage that fills the petro-occipital fissure. The anterolateral part of the inferior surface is pierced by the canals for the tensor tympani and the pharyngo-tympanic tube. The opening of the carotid canal and the jugular fossa are visible posteriorly on the inferior surface. The tympanic canaliculus pierces the inferior surface between the carotid canal and the jugular fossa. The cochlear canaliculus is located on the edge of the jugular fossa at the level of the anterior border of the petrous part, and the mastoid canaliculus is located laterally in the jugular fossa.
The posterior border, located between the inferior and the posterior surfaces, is grooved by the inferior petrosal sinus, and contributes to the jugular foramen. The anterior border, located between the inferior and the anterior surfaces, articulates with the greater wing of the sphenoid bone.

Squamous part

The thin anterosuperiorly located part, the external surface of which forms the medial wall of the temporal fossa, giving attachment to the temporalis muscle, and that is grooved by the middle temporal artery. The supramastoid crest, the suprameatal triangle, and the suprameatal spine (of Henle) are visible on the external surface. Occasionally, the squamo-mastoid suture can be seen approximately 1.5 cm below the supramastoid crest, and rarely the foramen for the petrosquamous sinus may persist above the posterior root of the zygomatic process. The concave internal surface of the squamous part is marked by the convolutions of the temporal lobe and the groove for the middle meningeal artery. The superior edge of the squama overlaps with the inferior border of the parietal bone. The inferior edge is rough internally and the anterior edge is rough externally in order to articulate with the greater wing of the sphenoid bone.

Tympanic part

The curved plate anterior to the mastoid process and inferior to the squamous part surrounding the external acoustic meatus. It fuses internally with the petrous part and posterosuperiorly with the squamous and mastoid parts. Anteriorly, the tympanic part is approximately rectangular constituting the tympanic plate, the medial part of which contributes to the squamo-tympanic fissure. The downward directed tegmen tympani protrudes as a crest from the squamo-tympanic fissure splitting it into petro-squamosal and petro-tympanic fissures. The sharp inferior edge of the tympanic part forms the vaginal process surrounding the base of the styloid process. The stylomastoid foramen is located between the styloid and the mastoid processes.

Styloid process

It arises from the inferior aspect of the temporal bone, typically showing an antero-medial concavity, and gives attachment to muscles and ligaments. Its dimension is variable, and its length can range between a few mm up to the average length of 25 mm.

Zygomatic process

It arises from the lower region of the squamous part with two roots, and projects anteriorly to articulate with the zygomatic bone. The inferior surface of the anterior root presents the articular tubercle, and its anterior border is in continuity with the infratemporal crest on the greater wing of the sphenoid bone. The mandibular fossa is visible posterior to the articular tubercle. Its anterior articular surface is separated from the posterior tympanic surface by the postglenoid tubercle. The squamo-tympanic fissure separates the mandibular fossa from the tympanic part. The posterior root continues posteriorly into the supramastoid crest.

ARTICULATIONS

The temporal bone articulates with the sphenoid, occipital, parietal, and zygomatic bones.

SKELETAL LANDMARKS

The tip of the mastoid process can be palpated behind the acoustic meatus. The lateral wall of the mastoid antrum corresponds to the suprameatal triangle, which is bounded by the posterosuperior margin of the acoustic meatus, the supramastoid crest, and a vertical line tangent to the posterior border of the acoustic meatus.

Anatomical Details

Arcuate Eminence

The convexity bulging from the superior surface of the petrous part. It corresponds to the position of the superior semicircular canal.

 

Articular Tubercle

The inferiorly directed semi-cylindrical convexity of the anterior root of the zygomatic process. It faces the temporo-mandibular joint, and is contact with the articular disc.

 

Carotid Canal

The canal that houses the internal carotid artery in its course from the neck to the cavernous sinus. Its anterior opening is at the apex of the petrous part, which is the posterolateral limit of the foramen lacerum. Its posterior opening is on the inferior surface of the petrous part. The carotid, which enters the temporal bone almost vertically, turns anteromedially during its course inside the bone to reach the apex.

 

Cochlear Canaliculus

A small canaliculus, housing the perilymphatic duct and a vein draining from the cochlea to the internal jugular vein, located anteromedial to the jugular fossa, and inferior to the internal acoustic meatus.

 

External Acoustic Meatus

The bony part of the external ear, that is located lateral to the middle ear. Its anterior wall, floor, and part of the posterior wall are formed by the tympanic part of the temporal bone. It is inferior to the squamous part, and anterior to the mastoid part of the temporal bone.

 

Greater Petrosal Nerve Foramen

A hole on the superior surface of the petrous part, anterior to the arcuate eminence. It is the exit point of the greater petrosal nerve, which branches from the facial nerve at the level of the geniculate ganglion.

 

Greater Petrosal Nerve Groove

The impression of the greater petrosal nerve on the petrous part, from the greater petrosal nerve foramen to the anterior opening of the carotid canal, where it joins the deep petrosal nerve forming the Vidian nerve.

 

Inferior Petrosal Sinus Sulcus

The notch on the posterior edge of the petrous part forming, together with the occipital bone, a sulcus for the inferior petrosal sinus.

 

Internal Acoustic Meatus

The opening, approximately at the center of the posterior surface of the petrous part, that gives access to the inner ear, and is traversed by the VII and VIII cranial nerves, together with the labyrinthine artery.

 

Jugular Fossa

The fossa behind the inferior petrosal sinus sulcus contributing with the occipital bone to form the jugular foramen.

 

Lesser Petrosal Nerve Foramen

A hole on the superior surface of the petrous part, anterior to the arcuate eminence, and lateral to the grater petrosal nerve foramen. It is the exit point of the lesser petrosal nerve, which arises from the tympanic plexus at the level of the middle ear.

 

Lesser Petrosal Nerve Groove

The impression of the lesser petrosal nerve on the petrous part, from the lesser petrosal nerve foramen to the foramen ovale, through which it exits the cranial cavity to reach the otic ganglion.

 

Mandibular Fossa

The fossa that houses the articular disk and the condyle of the mandible in the temporo-mandibular joint. It is limited anteriorly by the articular eminence, and posteriorly by the tympanic part of the temporal bone.

 

Mastoid Canaliculus

The canaliculus located in the lateral aspect of the jugular fossa, containing the auricular branch of the vagus nerve.

 

Mastoid Foramen

The variable foramen traversing the mastoid part of the temporal bone. It contains an emissary vein from the sigmoid sinus and a small dural branch of the occipital artery. In most cases, it is located just anterior to the posterior border of the mastoid part, although it can pierce the occipital bone or the occipito-mastoid suture, or it can be absent.

 

Mastoid Notch

A deep notch on the inferomedial surface of the mastoid process, lateral to the occipital groove for the occipital artery. It gives attachment to the digastric muscle. Synonym: Digastric notch.

 

Mastoid Process

The round, inferiorly directed process of the mastoid part of the temporal bone. It gives attachment to the longissimus capitis, splenius capitis, and sternocleidomastoid muscles on its lateral surface. It is larger in adult males.

 

Middle Meningeal Artery Groove

The impression of the middle meningeal artery on the internal surface of the squama of the temporal bone.

 

Middle Temporal Artery Groove

The impression of the middle temporal artery on the external surface of the squama of the temporal bone, superior to the external acoustic meatus.

 

Occipital Artery Meningeal Branch Groove

A small faint groove that can be visible arising from the internal end of the mastoid foramen. It bears the meningeal branch of the occipital artery.

 

Occipital Groove

The groove on the inferior surface of the mastoid part of the temporal bone, medial to the mastoid notch, bearing the occipital artery.

 

Petro-squamosal Fissure

The remainder of the suture between the petrous and the squamous parts of the temporal bone that fuse during the ossification process. Its traces are visible between the inferior border of the squamous part and the crest of the tegmen tympani arising from the petrous part. It is separated from the petro-tympanic fissure by the same crest.

 

Petro-squamosal Suture

The faint remainder of the suture between the petrous and the squamous parts of the temporal bone that fuse during the ossification process. It can be visible between the superior surface of the petrous part and the internal surface of the squamous part.

 

Petro-tympanic Fissure

The remainder of the suture between the tympanic and the petrous parts of the temporal bone that fuses during the ossification process. Its traces are visible inferiorly between the tympanic part and the crest of the tegmen tympani arising from the petrous part. It is separated from the petro-squamosal fissure by the same crest. It is traversed by part of the anterior ligament of the malleus, the anterior tympanic branch of the internal maxillary artery, and the chorda tympani arising from the facial nerve.

 

Pharyngo-tympanic Tube

The inferior of the two canals leading to the tympanic cavity that are visible at the junction between the squamous and the petrous parts of the temporal bone. It is the bony part of the Eustachian tube and opens into the tympanic cavity.

 

Post-glenoid Tubercle

The conical, lateral tubercle, inferior to the posterior root of the zygomatic process, separating the articular surface of the mandibular fossa from the tympanic plate.

 

Sigmoid Sinus Sulcus

The curved impression of the sigmoid sinus on the internal surface of the mastoid process. Its floor is constituted by a thin layer of bone separating it from the mastoid air cells.

 

Squamo-mastoid Suture

The faint remainder of the suture between the mastoid and the squamous parts of the temporal bone that fuse during the ossification process. It can be visible between the lateral surfaces of the mastoid and the squamous parts.

 

Squamo-tympanic Fissure

The remainder of the suture between the tympanic and the squamous parts of the temporal bone that fuse during the ossification process. Its traces are visible between the inferior border of the squamous part and the tympanic part. It is divided into petro-squamosal and petrotympanic fissures by the crest of the tegmen tympani.

 

Styloid Process

A pointed, variably long, anteroinferiorly directed process arising from the inferior aspect of the temporal bone. It usually shows an anteromedial concavity, although its curvature may vary. Its base is covered by a thin sheath from the tympanic plate; while its tip gives attachment to the styloglossus, stylohyoid, and stylopharyngeus muscles, and to the stylohyoid and stylomandibular ligaments.

 

Stylomastoid Foramen

The foramen located between the styloid and the mastoid processes constituting the external end of the facial canal. It is traversed by the facial nerve and the stylomastoid artery.

 

Subarcuate Canal

The small canal connecting the posterior cranial fossa to the mastoid antrum the mastoid antrum. It contains the subarcuate artery and vein.

 

Subarcuate Fossa

A depression on the posterior surface of the petrous part, located slightly superior to and between the internal acoustic meatus and the vestibular canaliculus.

 

Supramastoid Crest

The crest curving posterosuperiorly as the continuation of the posterior root of the zygomatic process. It crosses the posterior part of the squama, above the external acoustic meatus. It gives attachment to the deep temporal fascia.

 

Suprameatal Spine

The spine located inside the suprameatal triangle, just above the posterosuperior edge of the external acoustic meatus. Synonym: Spine of Henle.

 

Suprameatal Triangle

A triangular depression laying between the anterior end of the supramastoid crest and the posterosuperior quadrant of the external acoustic meatus. It constitutes the surface projection of the mastoid antrum.

 

Tegmen Tympani

The superior surface of the petrous part, constituting the roof of the tympanic cavity.

 

Tegmen Tympani Crest

The crest arising from the petrous part and reaching the inferior surface of the temporal into the squamo-tympanic fissure. It divides that fissure into petro-squamosal and petro-tympanic fissures.

 

Tensor Tympani Canal

The superior of the two canals leading to the tympanic cavity that are visible at the junction between the squamous and the petrous parts of the temporal bone. It houses the tensor tympani muscle.

 

Trigeminal Impression

The impression of the trigeminal ganglion on the superior border of the petrous part, behind its apex.

 

Tympanic Nerve Canaliculus

A canaliculus laying on the ridge between the jugular fossa and the carotid canal. It is traversed by the tympanic nerve arising from the glossopharyngeal nerve.

 

Tympanic Plate

The curved plate of bone of the tympanic part inferior to the squamous part and anterior to the mastoid process, to which it merges superiorly and posteriorly, respectively. It constitutes the posterior wall of the mandibular fossa, forming also the anterior wall, the floor, and part of the posterior wall of the external acoustic meatus.

 

Vaginal Process

The inferior border of the tympanic part splitting to form the sheath of the styloid process.

 

Vestibular Canaliculus

The canal located posterior to the internal acoustic meatus. It contains the endolymphatic sac and duct, together with small artery and vein.

 

Zygomatic Process

The process projecting anteriorly from the inferior portion of the squamous part. Its posterior, laterally directed base is triangular-shaped with superior and inferior surfaces, and anterior and posterior roots. The process turns anteromedially to reach the temporal process of the zygomatic bone and complete the zygomatic arch.

 

Zygomatic Process Anterior Root

The anterior root of the zygomatic process projecting horizontally from the squamous part. It is located above the articular tubercle.

 

Zygomatic Process Posterior Root

The posterior root of the zygomatic process projecting forwards from the supramastoid crest.

 

Vomer Bone

The vomer is thin, flat, and almost trapezoid. It forms the posteroinferior part of the nasal septum, dividing the nasal cavities, and presents two surfaces and four borders. The two surfaces present a groove for the nasopalatine nerve and vessels and many other minor grooves. The thick superior border shows the groove for the sphenoid rostrum between the alae. Each ala contributes to the vomerovaginal canal, which is completed by the vaginal process of the sphenoid bone. The anterior border presents a cleft for the septal cartilage. 

 

Full Description

ARTICULATIONS

The vomer bone articulates with the sphenoid, maxillary, palatine, and ethmoid bones.

Anatomical Details

Ala

Lateral projection arising from the thick superior border of the vomer. It inserts between the the body and the vaginal process of the sphenoid bone, giving also origin to the vomerovaginal canal.

 

Groove for Sphenoid Rostrum

A deep superior groove between the alae of the vomer for the articulation with the sphenoidal rostrum

 

Nasopalatine Groove

Prominent anteroinferiorly directed groove for the nasopalatine nerve and vessels.

 

Septal Cartilage Cleft

The sulcus for the articulation with the quadrangular cartilage of the septum.

 

Zygomatic Bone

The zygomatic bone is the main bone of the cheek. It forms part of the lateral wall and floor of the orbit, part of the zygomatic arch, and the anterior wall of the temporal and infratemporal fossae. It is roughly quadrangular and has three surfaces, five borders, and two processes, namely the frontal and the temporal processes. It articulates with the frontal, maxillary, sphenoid, and temporal bones.

 

Full Description

SHAPE

The zygomatic bone is the main bone of the cheek. It forms part of the lateral wall and the floor of the orbit, part of the zygomatic arch, and the anterior wall of the temporal and infratemporal fossae. It is roughly quadrangular and has three surfaces, five borders, and two processes, namely the frontal and the temporal processes.

PARTS
Body

The lateral surface is convex and pierced by the zygomatico-facial foramen near its orbital border. The orbital surface is smooth and concave, constituting the lateral wall and part of the inferior wall of the orbit, and it is marked by the zygomatico-orbital foramen. The lateral and the orbital surfaces are separated by a margin forming the inferolateral portion of the orbital opening. 
The zygomatic bone further constitutes the lateral edge of the inferior orbital fissure with the part located between the articulations with the maxillary and the sphenoid bones. The posteromedial surface shows a rough anterior part and a smooth, concave posterior part, which constitutes the anterior wall of the temporal fossa. It is pierced by the zygomatic-temporal foramen near the base of the frontal process. The lateral and the posteromedial surfaces are separated by the posterosuperior border, which is convex superiorly and concave inferiorly, and gives insertion to the deep temporal fascia in continuity with the frontal process. They are also separated by the posteroinferior border, that is roughened by the insertion of the masseter muscle, and by the anteroinferior border articulating with the maxillary bone. The anteroinferior border is directed superomedially and it reaches the orbital margin above the infraorbital foramen. 

Frontal process

The superiorly directed process arising from the zygomatic bone to articulate with the zygomatic process of the frontal bone. It constitutes part of the lateral wall of the orbit and the orbital rim. The marginal tubercle may be palpated on the posterosuperior border, inferior to the fronto-zygomatic suture. The Whitnall’s tubercle is typically present on the orbital aspect of the frontal process.

Temporal process

The posteriorly directed bony process arising from the body of the zygomatic bone. It articulates with the zygomatic process of the temporal bone to complete the zygomatic arch.

ARTICULATIONS

The zygomatic bone articulates with the frontal, maxillary, sphenoid, and temporal bones.

SKELETAL LANDMARKS

The superolateral borders of the face are defined by the frontal processes, which define also the lateral orbital rim. The malar eminence is the most prominent portion of the zygomatic bone, and the zygomatic arch is located posterior to it. 
The superior edge of the arch is parallel to the parietal branch of the middle meningeal artery, which lies on the transverse plane of the roof of the orbit, before turning superiorly at the level of the temporal bone. The pterion is located approximately 4 cm above the zygomatic arch and 3 cm behind the fronto-zygomatic suture. The pterion marks the Sylvian point and overlies the frontal branch of the middle meningeal artery.

Anatomical Details

Frontal Process

The superiorly directed process arising from the zygomatic bone to articulate with the zygomatic process of the frontal bone. It constitutes part of the lateral wall of the orbit and the orbital rim. Its convex posterior edge forms the vertical part of the posterosuperior temporal border of the zygomatic bone, which gives attachment to the deep temporal fascia.

 

Marginal Tubercle

A small tubercle located on the posterosuperior border of the frontal process. It is visible, and usually palpable, inferior to the fronto-zygomatic suture.

 

Temporal Process

The posteriorly directed bony process arising from the body of the zygomatic bone. It articulates with the zygomatic process of the temporal bone to complete the zygomatic arch. Its concave superior edge forms the horizontal part of the posterosuperior temporal border of the zygomatic bone, which gives attachment to the deep temporal fascia.

 

Whitnall Tubercle

A variable tubercle that is usually present on the orbital surface of frontal process. It is located inside the orbital cavity, approximately 1 cm inferior to the fronto-zygomatic suture. It gives attachment to part of the aponeurosis of levator palpebrae superioris muscle, the suspensory ligament of the eye, and the lateral palpebral ligament.

 

Zygomatico-facial Foramen

The foramen piercing the convex, lateral facial surface of the zygomatic bone. It is located near the anterior orbital border of the surface, sometimes being double or absent. It contains the zygomatico-facial neurovascular bundle reaching the outer surface of the skull.

 

Zygomatico-orbital Foramen

The foramen on the orbital surface of the zygomatic bone constituting the opening of the canals leading to the zygomatico-facial and zygomatico-temporal foramina.

 

Zygomatico-temporal Foramen

The foramen piercing the temporal surface of the zygomatic bone. It is located near the base of the frontal process, transmitting the zygomatico-temporal neurovascular bundle reaching the outer surface of the skull.

 

References

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Authors

 

Francesco Belotti, MD

Neurosurgery Resident
University of Brescia (Italy) 
"Spedali Civili" Hospital Brescia (Italy) 
Scientific Team - UpSurgeOn

 

Federico Nicolosi, MD

Neurosurgeon
University of Milan
"Spedali Civili" Hospital Brescia (Italy)
Scientific Team - UpSurgeOn