8
Head and Neck
Vestibulocochlear nerve [VIII]
Temporal and infratemporal fossae
Posterior triangle of the neck
Gaps in the pharyngeal wall and structures passing through them
ADDITIONAL LEARNING RESOURCES FOR CHAPTER 8, HEAD AND NECK, ON STUDENT CONSULT (www.studentconsult.com)
Image Library — illustrations of head and neck anatomy, Chapter 8
Self-Assessment — National Board style multiple-choice questions, Chapter 8
Short Questions — these are questions requiring short responses, Chapter 8
Interactive Surface Anatomy — interactive surface animations, Chapter 8
Medical Clinical Case Studies
Clinical CasesStenosis of the internal carotid artery
Posterior communicating artery aneurysm
Regional anatomy
The head and neck are anatomically complex areas of the body. The head is composed of a series of compartments, which are formed by bone and soft tissues (Fig. 8.1). They are:
the cranial cavity,
two ears,
two orbits,
two nasal cavities, and
an oral cavity.
Fig. 8.1 Overall design of head and neck.
The neck extends from the head above to the shoulders and thorax below (Fig. 8.1). The neck has four major compartments (Fig. 8.2), which are enclosed by an outer musculofascial collar:
The vertebral compartment contains the cervical vertebrae and associated postural muscles.
The visceral compartment contains important glands (thyroid, parathyroid, and thymus), and parts of the respiratory and digestive tracts (larynx and pharynx) that pass between the head and thorax.
The two vascular compartments, one on each side, contain the major blood vessels and the vagus nerve.
Fig. 8.2 Major compartments of the neck.
HEAD
Houses and protects the brain and all the receptor systems associated with the special senses—the nasal cavities associated with smell, the orbits with vision, the ears with hearing and balance, and the oral cavity with taste.
Contains the upper parts of the respiratory and digestive systems—the nasal and oral cavities—which have structural features for modifying the air or food passing into each system.NECK
Supports and positions the head. Importantly, it enables an individual to position sensory systems in the head relative to environmental cues without moving the entire body.
Contains specialized structures (pharynx and larynx) that connect the upper parts of the digestive and respiratory tracts (nasal and oral cavities) in the head, with the esophagus and trachea, which begin relatively low in the neck and pass into the thorax.The head and neck together function in communication. Sounds produced by the larynx are modified in the pharynx and oral cavity to produce speech. In addition, the muscles of facial expression adjust the contours of the face to relay nonverbal signals.
SKULL
The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which forms the lower jaw, the bones of the skull are attached to each other by sutures, are immobile, and form the cranium.
The cranium can be subdivided into:
an upper domed part (the calvaria), which covers the cranial cavity containing the brain;
a base that consists of the floor of the cranial cavity; and
a lower anterior part—the facial skeleton (viscerocranium).
The bones forming the calvaria are mainly the paired temporal and parietal bones, and parts of the unpaired frontal, sphenoid, and occipital bones.
The bones forming the base of the cranium are mainly parts of the sphenoid, temporal, and occipital bones.
The bones forming the facial skeleton are the paired nasal bones, palatine bones, lacrimal bones, zygomatic bones, maxillae, inferior nasal conchae, and the unpaired vomer.
The mandible is not part of the cranium nor part of the facial skeleton.
Anterior view
The anterior view of the skull includes the forehead superiorly, and, inferiorly, the orbits, the nasal region, the part of the face between the orbit and the upper jaw, the upper jaw, and the lower jaw (Fig. 8.3; also see Fig. 8.4).
Fig. 8.3 Anterior view of the skull.
Imaging app
Visualizing the skull—anterior view
Fig. 8.4 Volume-rendered anterior view using multidetector computed tomography.
Frontal bone
The forehead consists of the frontal bone, which also forms the superior part of the rim of each orbit (Fig. 8.3).
Just superior to the rim of the orbit on each side are the raised superciliary arches. These are more pronounced in men than in women. Between these arches is a small depression (the glabella).
Clearly visible in the medial part of the superior rim of each orbit is the supra-orbital foramen (supra-orbital notch; Table 8.1).
Table 8.1 External foramina of the skull
|
Foramen |
Structures passing through foramen |
|
Anterior view |
|
|
Supra-orbital foramen |
Supra-orbital nerve and vessels |
|
Infra-orbital foramen |
Infra-orbital nerve and vessels |
|
Mental foramen |
Mental nerve and vessels |
|
Lateral view |
|
|
Zygomaticofacial foramen |
Zygomaticofacial nerve |
|
Superior view |
|
|
Parietal foramen |
Emissary veins |
|
Inferior view |
|
|
Incisive foramina |
Nasopalatine nerve; sphenopalatine vessels |
|
Greater palatine foramen |
Greater palatine nerve and vessels |
|
Lesser palatine foramina |
Lesser palatine nerve and vessels |
|
Pterygoid canal |
Pterygoid nerve and vessels |
|
Foramen ovale |
Mandibular nerve [V3]; lesser petrosal nerve |
|
Foramen spinosum |
Middle meningeal artery |
|
Foramen lacerum |
Filled with cartilage |
|
Carotid canal |
Internal carotid artery and nerve plexus |
|
Foramen magnum |
Continuation of brain and spinal cord; vertebral arteries and nerve plexuses; anterior spinal artery; posterior spinal arteries; roots of accessory nerve [XI]; meninges |
|
Condylar canal |
Emissary veins |
|
Hypoglossal canal |
Hypoglossal nerve [XII] and vessels |
|
Jugular foramen |
Internal jugular vein; inferior petrosal sinus; glossopharyngeal nerve [IX]; vagus nerve [X]; accessory nerve [XI] |
|
Stylomastoid foramen |
Facial nerve [VII] |
Medially, the frontal bone projects inferiorly forming a part of the medial rim of the orbit.
Laterally, the zygomatic process of the frontal bone projects inferiorly, forming the upper lateral rim of the orbit. This process articulates with the frontal process of the zygomatic bone.
Zygomatic and nasal bones
The lower lateral rim of the orbit, as well as the lateral part of the inferior rim of the orbit, is formed by the zygomatic bone (the cheekbone) (Fig. 8.3).
Superiorly, in the nasal region, the paired nasal bones articulate with each other in the midline and with the frontal bone superiorly. The center of the frontonasal suture formed by the articulation of the nasal bones and the frontal bone is the nasion.
Laterally, each nasal bone articulates with the frontal process of each maxilla.
Inferiorly, the piriform aperture is the large opening in the nasal region and the anterior opening of the nasal cavity. It is bounded superiorly by the nasal bones and laterally and inferiorly by each maxilla.
Visible through the piriform aperture are the fused nasal crests, forming the lower part of the bony nasal septum and ending anteriorly as the anterior nasal spine, and the paired inferior nasal conchae
Maxillae
The part of the face between the orbit and the upper teeth and each upper jaw is formed by the paired maxillae (Fig. 8.3).
Superiorly, each maxilla contributes to the inferior and medial rims of the orbit.
Laterally, the zygomatic process of each maxilla articulates with the zygomatic bone and medially, the frontal process of each maxilla articulates with the frontal bone.
Inferiorly, the part of each maxilla, lateral to the opening of the nasal cavity, is the body of maxilla.
On the anterior surface of the body of maxilla, just below the inferior rim of the orbit, is the infra-orbital foramen (Table 8.1).
Inferiorly, each maxilla ends as the alveolar process, which contains the teeth and forms the upper jaw.
Mandible
The lower jaw (mandible) is the most inferior structure in the anterior view of the skull (see Fig. 8.3). It consists of the body of mandible anteriorly and the ramus of mandible posteriorly. These meet posteriorly at the angle of mandible. All these parts of the mandible are visible, to some extent, in the anterior view.
The body of mandible is arbitrarily divided into two parts:
The lower part is the base of mandible.
The upper part is the alveolar part of mandible
The alveolar part of mandible contains the teeth and is resorbed when the teeth are removed. The base of mandible has a midline swelling (the mental protuberance) on its anterior surface where the two sides of the mandible come together. Just lateral to the mental protuberance, on either side, are slightly more pronounced bumps (mental tubercles).
Laterally, a mental foramen (see Table 8.1) is visible halfway between the upper border of the alveolar part of mandible and the lower border of the base of mandible. Continuing past this foramen is a ridge (the oblique line) passing from the front of the ramus onto the body of mandible. The oblique line is a point of attachment for muscles that depress the lower lip.
Lateral view
The lateral view of the skull consists of the lateral wall of the cranium, which includes lateral portions of the calvaria and the facial skeleton, and half of the lower jaw (Fig. 8.5; see also Fig. 8.6):
Bones forming the lateral portion of the calvaria include the frontal, parietal, occipital, sphenoid, and temporal bones.
Bones forming the visible part of the facial skeleton include the nasal, maxilla, and zygomatic bones.
The mandible forms the visible part of the lower jaw.
Fig. 8.5 Lateral view of the skull.
Imaging app
Visualizing the skull—lateral view
Fig. 8.6 Volume-rendered lateral view using multidetector computed technology.
Lateral portion of the calvaria
The lateral portion of the calvaria begins anteriorly with the frontal bone. In upper regions, the frontal bone articulates with the parietal bone at the coronal suture (Fig. 8.5). The parietal bone then articulates with the occipital bone at the lambdoid suture.
In lower parts of the lateral portion of the calvaria, the frontal bone articulates with the greater wing of sphenoid bone (Fig. 8.5), which then articulates with the parietal bone at the sphenoparietal suture, and with the anterior edge of the temporal bone at the sphenosquamous suture.
The junction where the frontal, parietal, sphenoid, and temporal bones are in close proximity is the pterion (Fig. 8.5). The clinical consequences of a skull fracture in this area can be very serious. The bone in this area is particularly thin and overlies the anterior division of the middle meningeal artery, which can be torn by a skull fracture in this area, resulting in an extradural hematoma.
The final articulation across the lower part of the lateral portion of the calvaria is between the temporal bone and the occipital bone at the occipitomastoid suture (Fig. 8.5).
Temporal bone
A major contributor to the lower portion of the lateral wall of the cranium is the temporal bone (Fig. 8.5), which consists of several parts:
The squamous part has the appearance of a large flat plate, forms the anterior and superior parts of the temporal bone, contributes to the lateral wall of the cranium, and articulates anteriorly with the greater wing of the sphenoid bone at the sphenosquamous suture, and with the parietal bone superiorly at the squamous suture.
The zygomatic process is an anterior bony projection from the lower surface of the squamous part of the temporal bone that initially projects laterally and then curves anteriorly to articulate with the temporal process of the zygomatic bone to form the zygomatic arch.
Immediately below the origin of the zygomatic process from the squamous part of the temporal bone is the tympanic part of the temporal bone, and clearly visible on the surface of this part is the external acoustic opening leading to the external acoustic meatus (ear canal).
The petromastoid part, which is usually separated into a petrous part and a mastoid part for descriptive purposes.The mastoid part is the most posterior part of the temporal bone, and is the only part of the petromastoid part of the temporal bone seen on a lateral view of the skull. It is continuous with the squamous part of the temporal bone anteriorly, and articulates with the parietal bone superiorly at the parietomastoid suture, and with the occipital bone posteriorly at the occipitomastoid suture. These two sutures are continuous with each other, and the parietomastoid suture is continuous with the squamous suture.
Inferiorly, a large bony prominence (the mastoid process) projects from the inferior border of the mastoid part of the temporal bone (Fig. 8.5). This is a point of attachment for several muscles.
Medial to the mastoid process, the styloid process projects from the lower border of the temporal bone.
Visible part of the facial skeleton
The bones of the viscerocranium visible in a lateral view of the skull include the nasal, maxilla, and zygomatic bones (Fig. 8.5) as follows:
a nasal bone anteriorly;
the maxilla with its alveolar process containing teeth forming the upper jaw; anteriorly, it articulates with the nasal bone; superiorly, it contributes to the formation of the inferior and medial borders of the orbit; medially, its frontal process articulates with the frontal bone; laterally, its zygomatic process articulates with the zygomatic bone;
the zygomatic bone, an irregularly shaped bone with a rounded lateral surface that forms the prominence of the cheek, is a visual centerpiece in this view; medially, it assists in the formation of the inferior rim of the orbit through its articulation with the zygomatic process of the maxilla; superiorly, its frontal process articulates with the zygomatic process of the frontal bone assisting in the formation of the lateral rim of the orbit; laterally, seen prominently in this view of the skull, the horizontal temporal process of the zygomatic bone projects backward to articulate with the zygomatic process of the temporal bone and so form the zygomatic arch.Usually a small foramen (the zygomaticofacial foramen; see Table 8.1) is visible on the lateral surface of the zygomatic bone. A zygomaticotemporal foramen is present on the medial deep surface of the bone.
Mandible
The final bony structure visible in a lateral view of the skull is the mandible. Inferiorly in the anterior part of this view, it consists of the anterior body of mandible, a posterior ramus of mandible, and the angle of mandible where the inferior margin of the mandible meets the posterior margin of the ramus (Fig. 8.5).
The teeth are in the alveolar part of the body of mandible and the mental protuberance is visible in this view.
The mental foramen is on the lateral surface of the body and on the superior part of the ramus, a condylar and coronoid process extend upward.
The condylar process is involved in articulation of the mandible with the temporal bone, and the coronoid process is the point of attachment for the temporalis muscle.
Anatomical position of the head and major landmarks
The head is in the anatomical position when the inferior margins of the bony orbits and the superior margins of the external acoustic meatuses are in the same horizontal plane (Frankfort plane).
In addition to the external acoustic meatus and the bony margin of the orbit, other features that are palpable include the head of mandible, zygomatic arch, zygomatic bone, mastoid process, and external occipital protuberance (Fig. 8.7).
Fig. 8.7 Anatomical position of the head and major landmarks. Lateral head and neck of a man.
The head of mandible is anterior to the external ear and behind and inferior to the posterior end of the zygomatic arch. It is best found by opening and closing the jaw and palpating the head of mandible as it moves forward onto the articular tubercle and then back into the mandibular fossa, respectively.
The zygomatic arch extends forward from the region of the temporomandibular joint to the zygomatic bone, which forms a bony prominence lateral to the inferior margin of the anterior opening of the orbit.
The mastoid process is a large bony protuberance that is easily palpable posterior to the inferior aspect of the external acoustic meatus. The superior end of the sternocleidomastoid muscle attaches to the mastoid process.
The external occipital protuberance is palpable in the midline posteriorly where the contour of the skull curves sharply forward. This landmark marks the point superficially where the back of the neck joins the head.
Another clinically useful feature of the head is the vertex. This is the highest point of the head in the anatomical position and marks the approximate point on the scalp where there is a transition from cervical to cranial innervation of the scalp. Anterior to the vertex the scalp and face are innervated by the trigeminal nerve [V]. Posterior to the vertex, the scalp is innervated by branches from cervical spinal nerves.
Posterior view
The occipital, parietal, and temporal bones are seen in the posterior view of the skull (Fig. 8.8).
Fig. 8.8 Posterior view of the skull.
Occipital bone
Centrally the flat or squamous part of occipital bone is the main structure in this view of the skull (Fig. 8.8). It articulates superiorly with the paired parietal bones at the lambdoid suture and laterally with each temporal bone at the occipitomastoid sutures. Along the lambdoid suture, small islands of bone (sutural bones or wormian bones) may be observed.
Several bony landmarks are visible on the occipital bone. There is a midline projection, (the external occipital protuberance) with curved lines extending laterally from it (superior nuchal lines). The most prominent point of the external occipital protuberance is the inion. About 1 inch (2.5 cm) below the superior nuchal lines, two additional lines (the inferior nuchal lines) curve laterally. Extending downward from the external occipital protuberance is the external occipital crest.
Temporal bones
Laterally, the temporal bones are visible in the posterior view of the skull, with the mastoid processes being the prominent feature (Fig. 8.8). On the inferomedial border of each mastoid process is a notch (the mastoid notch), which is a point of attachment for the posterior belly of the digastric muscle.
Superior view
The frontal bone, parietal bones, and occipital bone are seen in a superior view of the skull (Fig. 8.9). These bones make up the superior part of the calvaria, or the calva (skullcap).
Fig. 8.9 Superior view of the skull.
In an anterior to posterior direction:
The unpaired frontal bone articulates with the paired parietal bones at the coronal suture.
The two parietal bones articulate with each other in the midline at the sagittal suture.
The parietal bones articulate with the unpaired occipital bone at the lambdoid suture.
The junction of the sagittal and coronal sutures is the bregma, and the junction of the sagittal and lambdoid sutures is the lambda.
The only foramen visible in this view of the skull may be the paired parietal foramina; posteriorly, one on each parietal bone just lateral to the sagittal suture (Fig. 8.9).
The bones making up the calvaria (Fig. 8.10) are unique in their structure, consisting of dense internal and external tables of compact bone separated by a layer of spongy bone (the diploë).
Fig. 8.10 Calvaria.
Inferior view
The base of the skull is seen in the inferior view and extends anteriorly from the middle incisor teeth posteriorly to the superior nuchal lines and laterally to the mastoid processes and zygomatic arches (Fig. 8.11).
Fig. 8.11 Inferior view of the skull.
For descriptive purposes, the base of the skull is often divided into:
an anterior part, which includes the teeth and the hard palate;
a middle part, which extends from behind the hard palate to the anterior margin of the foramen magnum; and
a posterior part, which extends from the anterior edge of the foramen magnum to the superior nuchal lines.Anterior part
The main features of the anterior part of the base of the skull are the teeth and the hard palate.
The teeth project from the alveolar processes of the two maxillae. These processes are arranged together in a U-shaped alveolar arch that borders the hard palate on three sides (Fig. 8.11).
The hard palate is composed of the palatine processes of each maxilla anteriorly and the horizontal plates of each palatine bone posteriorly.
The paired palatine processes of each maxilla meet in the midline at the intermaxillary suture, the paired maxilla and the paired palatine bones meet at the palatomaxillary suture, and the paired horizontal plates of each palatine bone meet in the midline at the interpalatine suture.
Several additional features are also visible when the hard palate is examined:
The incisive fossa in the anterior midline immediately posterior to the teeth, the walls of which contain incisive foramina (the openings of the incisive canals, which are passageways between the hard palate and nasal cavity).
The greater palatine foramina near the posterolateral border of the hard palate on each side, which lead to greater palatine canals.
Just posterior to the greater palatine foramina, the lesser palatine foramina in the pyramidal process of each palatine bone, which lead to lesser palatine canals.
A midline pointed projection (the posterior nasal spine) in the free posterior border of the hard palate.Middle part
The middle part of the base of the skull is complex:
Forming the anterior half are the vomer and sphenoid bones.
Forming the posterior half are the occipital and paired temporal bones.
Anterior half
Anteriorly, the small vomer is in the midline, resting on the sphenoid bone (Fig. 8.11). It contributes to the formation of the bony nasal septum separating the two choanae.
Most of the anterior part of the middle part of the base of the skull consists of the sphenoid bone.
The sphenoid bone is made up of a centrally placed body, paired greater and lesser wings projecting laterally from the body, and two downward projecting pterygoid processes immediately lateral to each choana.
Three parts of the sphenoid bone, the body, greater wings, and pterygoid processes, are seen in the inferior view of the skull (Fig. 8.11). The lesser wing of the sphenoid is not seen in the inferior view.
The body of the sphenoid is a centrally placed cube of bone containing two large air sinuses separated by a septum.
It articulates anteriorly with the vomer, ethmoid, and palatine bones, posterolaterally with the temporal bones, and posteriorly with the occipital bone.
Extending downward from the junction of the body and the greater wings are the pterygoid processes (Fig. 8.11). Each of these processes consists of a narrow medial plate and broader lateral plate separated by the pterygoid fossa.
Each medial plate of the pterygoid process ends inferiorly with a hook-like projection, the pterygoid hamulus, and divides superiorly to form the small, shallow scaphoid fossa.
Just superior to the scaphoid fossa, at the root of the medial plate of the pterygoid process is the opening of the pterygoid canal, which passes forward from near the anterior margin of the foramen lacerum.
Lateral to the lateral plate of the pterygoid process is the greater wing of the sphenoid (Fig. 8.11), which not only forms a part of the base of the skull, but also continues laterally to form part of the lateral wall of the skull. It articulates laterally and posteriorly with parts of the temporal bone.
Important features visible on the surface of the greater wing in an inferior view of the skull are the foramen ovale and the foramen spinosum on the posterolateral border extending outward from the upper end of the lateral plate of the pterygoid process.
Posterior half of middle part
In the posterior half of the middle part of the base of the skull are the occipital bone and the paired temporal bones (Fig. 8.11).
The occipital bone, or more specifically its basilar part, is in the midline immediately posterior to the body of the sphenoid. It extends posteriorly to the foramen magnum and is bounded laterally by the temporal bones.
Prominent on the basilar part of the occipital bone is the pharyngeal tubercle, a bony protuberance for the attachment of parts of the pharynx to the base of the skull (Fig. 8.11).
Immediately lateral to the basilar part of the occipital bone is the petrous part of the petromastoid part of each temporal bone.
Wedge-shaped in its appearance, with its apex anteromedial, the petrous part of the temporal bone is between the greater wing of the sphenoid anteriorly and the basilar part of the occipital bone posteriorly. The apex forms one of the boundaries of the foramen lacerum, an irregular opening filled in life with cartilage (Fig. 8.11).
The other boundaries of the foramen lacerum are the basilar part of the occipital bone medially and the body of the sphenoid anteriorly.
Posterolateral from the foramen lacerum along the petrous part of the temporal bone is the large circular opening for the carotid canal.
Between the petrous part of the temporal bone and the greater wing of the sphenoid is a groove for the cartilaginous part of the pharyngotympanic tube (auditory tube). This groove continues posterolaterally into a bony canal in the petrous part of the temporal bone for the pharyngotympanic tube.
Just lateral to the greater wing of the sphenoid is the squamous part of the temporal bone, which participates in the temporomandibular joint. It contains the mandibular fossa, which is a concavity where the head of the mandible articulates with the base of the skull. An important feature of this articulation is the prominent articular tubercle, which is the downward projection of the anterior border of the mandibular fossa (Fig. 8.11).
Posterior part
The posterior part of the base of the skull extends from the anterior edge of the foramen magnum posteriorly to the superior nuchal lines (Fig. 8.11). It consists of parts of the occipital bone centrally and the temporal bones laterally.
Occipital bone
The occipital bone is the major bony element of this part of the base of the skull (Fig. 8.11). It has four parts organized around the foramen magnum, which is a prominent feature of this part of the base of the skull and through which the brain and spinal cord are continuous.
The parts of the occipital bone are the squamous part, which is posterior to the foramen magnum, the lateral parts, which are lateral to the foramen magnum, and the basilar part, which is anterior to the foramen magnum (Fig. 8.11).
The squamous and lateral parts are components of the posterior part of the base of the skull.
The most visible feature of the squamous part of the occipital bone, when examining the inferior view of the skull, is a ridge of bone (the external occipital crest) that extends downward from the external occipital protuberance toward the foramen magnum. The inferior nuchal lines arc laterally from the midpoint of the crest.
Immediately lateral to the foramen magnum are the lateral parts of the occipital bones, which contain numerous important structural features.
On each anterolateral border of the foramen magnum are the rounded occipital condyles (Fig. 8.11). These paired structures articulate with the atlas (vertebra CI). Posterior to each condyle is a depression (the condylar fossa) containing a condylar canal, and anterior and superior to each condyle is the large hypoglossal canal. Lateral to each hypoglossal canal is a large, irregular jugular foramen formed by opposition of the jugular notch of the occipital bone and jugular notch of the temporal bone.
Temporal bone
Laterally in the posterior part of the base of the skull is the temporal bone. The parts of the temporal bone seen in this location are the mastoid part of the petromastoid part and the styloid process (see Fig. 8.11).
The lateral edge of the mastoid part is identified by the large cone-shaped mastoid process projecting from its inferior surface. This prominent bony structure is the point of attachment for several muscles. On the medial aspect of the mastoid process is the deep mastoid notch, which is also an attachment point for a muscle.
Anteromedial to the mastoid process is the needle-shaped styloid process projecting from the lower border of the temporal bone. The styloid process is also a point of attachment for numerous muscles and ligaments.
Finally, between the styloid process and the mastoid process is the stylomastoid foramen.
CRANIAL CAVITY
The cranial cavity is the space within the cranium that contains the brain, meninges, proximal parts of the cranial nerves, blood vessels, and cranial venous sinuses.
Roof
The calvaria is the dome-shaped roof that protects the superior aspect of the brain. It consists mainly of the frontal bone anteriorly, the paired parietal bones in the middle, and the occipital bone posteriorly (Fig. 8.12).
Fig. 8.12 Roof of the cranial cavity.
Sutures visible internally include:
the coronal suture, between the frontal and parietal bones;
the sagittal suture, between the paired parietal bones; and
the lambdoid suture, between the parietal and occipital bones.
Visible junctions of these sutures are the bregma, where the coronal and sagittal sutures meet, and the lambda, where the lambdoid and sagittal sutures meet.
Other markings on the internal surface of the calva include bony ridges, and numerous grooves and pits (Fig. 8.12).
From anterior to posterior, features seen on the bony roof of the cranial cavity are (Fig. 8.12):
a midline ridge of bone extending from the surface of the frontal bone (the frontal crest), which is a point of attachment for the falx cerebri (a specialization of the dura mater that partially separates the two cerebral hemispheres);
at the superior point of the termination of the frontal crest the beginning of the groove for the superior sagittal sinus, which widens and deepens posteriorly and marks the position of the superior sagittal sinus (an intradural venous structure);
on either side of the groove for the superior sagittal sinus throughout its course, a small number of depressions and pits (the granular foveolae), which mark the location of arachnoid granulations (prominent structures readily identifiable when a brain with its meningeal coverings is examined; the arachnoid granulations are involved in the reabsorption of cerebrospinal fluid); and
on the lateral aspects of the roof of the cranial cavity, smaller grooves created by various meningeal vessels.Floor
The floor of the cranial cavity is divided into anterior, middle, and posterior cranial fossae.
Anterior cranial fossa
Parts of the frontal, ethmoid, and sphenoid bones form the anterior cranial fossa (Fig. 8.13). Its floor is composed of:
frontal bone in the anterior and lateral direction;
ethmoid bone in the midline; and
two parts of the sphenoid bone posteriorly, the body (midline), and the lesser wings (laterally).
Fig. 8.13 Anterior cranial fossa.
The anterior cranial fossa is above the nasal cavity and the orbits, and it is filled by the frontal lobes of the cerebral hemispheres.
Anteriorly, a small wedge-shaped midline crest of bone (the frontal crest) projects from the frontal bone. This is a point of attachment for the falx cerebri. Immediately posterior to the frontal crest is the foramen cecum (Table 8.2). This foramen between the frontal and ethmoid bones may transmit emissary veins connecting the nasal cavity with the superior sagittal sinus.
Table 8.2 Internal foramina of the skull
|
Foramen |
Structures passing through foramen |
|
Anterior cranial fossa |
|
|
Foramen cecum |
Emissary veins to nasal cavity |
|
Olfactory foramina in cribriform plate |
Olfactory nerves [I] |
|
Middle cranial fossa |
|
|
Optic canal |
Optic nerve [II]; ophthalmic artery |
|
Superior orbital fissure |
Oculomotor nerve [III]; trochlear nerve [IV]; ophthalmic division of the trigeminal nerve [V1]; abducent nerve [VI]; ophthalmic veins |
|
Foramen rotundum |
Maxillary division of the trigeminal nerve [V2] |
|
Foramen ovale |
Mandibular division of the trigeminal nerve [V3]; lesser petrosal nerve |
|
Foramen spinosum |
Middle meningeal artery |
|
Hiatus for the greater petrosal nerve |
Greater petrosal nerve |
|
Hiatus for the lesser petrosal nerve |
Lesser petrosal nerve |
|
Posterior cranial fossa |
|
|
Foramen magnum |
End of brainstem/beginning of spinal cord; vertebral arteries; spinal roots of the accessory nerve; meninges |
|
Internal acoustic meatus |
Facial nerve [VII]; vestibulocochlear nerve [VIII]; labyrinthine artery |
|
Jugular foramen |
Glossopharyngeal nerve [IX]; vagus nerve [X]; accessory nerve [XI]; inferior petrosal sinus, sigmoid sinus (forming internal jugular vein) |
|
Hypoglossal canal |
Hypoglossal nerve [XII]; meningeal branch of the ascending pharyngeal artery |
|
Condylar canal |
Emissary vein |
Posterior to the frontal crest is a prominent wedge of bone projecting superiorly from the ethmoid (the crista galli). This is another point of attachment for the falx cerebri, which is the vertical extension of dura mater partially separating the two cerebral hemispheres.
Lateral to the crista galli is the cribriform plate of the ethmoid bone (see Fig. 8.13). This is a sieve-like structure, which allows small olfactory nerve fibers to pass through its foramina from the nasal mucosa to the olfactory bulb. The olfactory nerves are commonly referred to collectively as the olfactory nerve [I].
