Head and Neck

Published on 17/03/2015 by admin

Filed under Basic Science

Last modified 17/03/2015

Print this page

This article have been viewed 11699 times

Head and Neck

ADDITIONAL LEARNING RESOURCES for Chapter 8, Head and Neck, on STUDENT CONSULT (www.studentconsult.com):

Conceptual overview

General description

The head and neck are anatomically complex areas of the body.

Head

Major compartments

The head is composed of a series of compartments, which are formed by bone and soft tissues. They are:

the cranial cavity,

two ears,

two orbits,

two nasal cavities, and

an oral cavity (Fig. 8.1).

Fig. 8.1 Major compartments of the head and neck.

The cranial cavity is the largest compartment and contains the brain and associated membranes (meninges).

Most of the ear apparatus on each side is contained within one of the bones forming the floor of the cranial cavity. The external parts of the ears extend laterally from these regions.

The two orbits contain the eyes. They are cone-shaped chambers immediately inferior to the anterior aspect of the cranial cavity, and the apex of each cone is directed posteromedially. The walls of the orbits are bone, whereas the base of each conical chamber can be opened and closed by the eyelids.

The nasal cavities are the upper parts of the respiratory tract and are between the orbits. They have walls, floors, and ceilings, which are predominantly composed of bone and cartilage. The anterior openings to the nasal cavities are nares (nostrils), and the posterior openings are choanae (posterior nasal apertures).

Continuous with the nasal cavities are air-filled extensions (paranasal sinuses), which project laterally, superiorly, and posteriorly into surrounding bones. The largest, the maxillary sinuses, are inferior to the orbits.

The oral cavity is inferior to the nasal cavities, and separated from them by the hard and soft palates. The floor of the oral cavity is formed entirely of soft tissues.

The anterior opening to the oral cavity is the oral fissure (mouth), and the posterior opening is the oropharyngeal isthmus. Unlike the nares and choanae, which are continuously open, both the oral fissure and oropharyngeal isthmus can be opened and closed by surrounding soft tissues.

Other anatomically defined regions

In addition to the major compartments of the head, two other anatomically defined regions (infratemporal fossa and pterygopalatine fossa) of the head on each side are areas of transition from one compartment of the head to another (Fig. 8.2). The face and scalp also are anatomically defined areas of the head and are related to external surfaces.

Fig. 8.2 Areas of transition from one compartment of the head to another.

The infratemporal fossa is an area between the posterior aspect (ramus) of the mandible and a flat region of bone (lateral plate of the pterygoid process) just posterior to the upper jaw (maxilla). This fossa, bounded by bone and soft tissues, is a conduit for one of the major cranial nerves—the mandibular nerve (the mandibular division of the trigeminal nerve [V₃]), which passes between the cranial and oral cavities.

The pterygopalatine fossa on each side is just posterior to the upper jaw. This small fossa communicates with the cranial cavity, the infratemporal fossa, the orbit, the nasal cavity, and the oral cavity. A major structure passing through the pterygopalatine fossa is the maxillary nerve (the maxillary division of the trigeminal nerve [V₂]).

The face is the anterior aspect of the head and contains a unique group of muscles that move the skin relative to underlying bone and control the anterior openings to the orbits and oral cavity (Fig. 8.3).

The scalp covers the superior, posterior, and lateral regions of the head (Fig. 8.3).

The neck extends from the head above to the shoulders and thorax below (Fig. 8.4). Its superior boundary is along the inferior margins of the mandible and bone features on the posterior aspect of the skull. The posterior neck is higher than the anterior neck to connect cervical viscera with the posterior openings of the nasal and oral cavities.

The inferior boundary of the neck extends from the top of the sternum, along the clavicle, and onto the adjacent acromion, a bony projection of the scapula. Posteriorly, the inferior limit of the neck is less well defined, but can be approximated by a line between the acromion and the spinous process of vertebra CVII, which is prominent and easily palpable. The inferior border of the neck encloses the base of the neck.

Compartments

The neck has four major compartments (Fig. 8.5), 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 that pass between the head and thorax.

The two vascular compartments, one on each side, contain the major blood vessels and the vagus nerve.

Larynx and pharynx

The neck contains two specialized structures associated with the digestive and respiratory tracts—the larynx and pharynx.

The larynx (Fig. 8.6) is the upper part of the lower airway and is attached below to the top of the trachea and above, by a flexible membrane, to the hyoid bone, which in turn is attached to the floor of the oral cavity. A number of cartilages form a supportive framework for the larynx, which has a hollow central channel. The dimensions of this central channel can be adjusted by soft tissue structures associated with the laryngeal wall. The most important of these are two lateral vocal folds, which project toward each other from adjacent sides of the laryngeal cavity. The upper opening of the larynx (laryngeal inlet) is tilted posteriorly, and is continuous with the pharynx.

Fig. 8.6 Specialized structures of the neck. A. Conceptual view. B. Anatomical view.

The pharynx (Fig. 8.6) is a chamber in the shape of a half-cylinder with walls formed by muscles and fascia. Above, the walls are attached to the base of the skull, and below to the margins of the esophagus. On each side, the walls are attached to the lateral margins of the nasal cavities, the oral cavity, and the larynx. The two nasal cavities, the oral cavity, and the larynx therefore open into the anterior aspect of the pharynx, and the esophagus opens inferiorly.

The part of the pharynx posterior to the nasal cavities is the nasopharynx. Those parts posterior to the oral cavity and larynx are the oropharynx and laryngopharynx, respectively.

Functions

Component parts

Skull

The many bones of the head collectively form the skull (Fig. 8.7A). Most of these bones are interconnected by sutures, which are immovable fibrous joints (Fig. 8.7B).

Fig. 8.7 Skull. A. Bones. B. Sutures. C. Fontanelles and lambdoid suture.

In the fetus and newborn, large membranous and unossified gaps (fontanelles) between the bones of the skull, particularly between the large flat bones that cover the top of the cranial cavity (Fig. 8.7C), allow:

the head to deform during its passage through the birth canal, and

postnatal growth.

Most of the fontanelles close during the first year of life. Full ossification of the thin connective tissue ligaments separating the bones at the suture lines begins in the late twenties, and is normally completed in the fifth decade of life.

There are only three pairs of synovial joints on each side in the head. The largest are the temporomandibular joints between the lower jaw (mandible) and the temporal bone. The other two synovial joints are between the three tiny bones in the middle ear, the malleus, incus, and stapes.

Cervical vertebrae

The seven cervical vertebrae form the bony framework of the neck.

Cervical vertebrae (Fig. 8.8A) are characterized by:

Fig. 8.8 Cervical vertebrae. A. Typical features. B. Atlas—vertebra CI (superior view). C. Axis—vertebra CII (anterior view). D. Atlas and axis (anterolateral view). E. Atlanto-occipital joint (posterior view).

small bodies,

bifid spinous processes, and

transverse processes that contain a foramen (foramen transversarium).

Together the foramina transversaria form a longitudinal passage on each side of the cervical vertebral column for blood vessels (vertebral artery and veins) passing between the base of the neck and the cranial cavity.

The typical transverse process of a cervical vertebra also has anterior and posterior tubercles for muscle attachment. The anterior tubercles are derived from the same embryological elements that give rise to ribs in the thoracic region. Occasionally, cervical ribs develop from these elements, particularly in association with the lower cervical vertebrae.

The upper two cervical vertebrae (CI and CII) are modified for moving the head (Fig. 8.8B–E; see also Chapter 2).

Hyoid bone

The hyoid bone is a small U-shaped bone (Fig. 8.9A) oriented in the horizontal plane just superior to the larynx, where it can be palpated and moved from side to side.

Fig. 8.9 Hyoid. A. Bone. B. Attachments.

The body of the hyoid bone is anterior and forms the base of the U.

The two arms of the U (greater horns) project posteriorly from the lateral ends of the body.

The hyoid bone does not articulate directly with any other skeletal elements in the head and neck.

The hyoid bone is a highly movable and strong bony anchor for a number of muscles and soft tissue structures in the head and neck. Significantly, it is at the interface between three dynamic compartments:

Superiorly, it is attached to the floor of the oral cavity.

Inferiorly, it is attached to the larynx.

Posteriorly, it is attached to the pharynx (Fig. 8.9B).

Soft palate

The soft palate is a soft tissue flap-like structure “hinged” to the back of the hard palate (Fig. 8.10A) with a free posterior margin. It can be elevated and depressed by muscles (Fig. 8.10B).

The soft palate and associated structures can be clearly seen through an open mouth.

Muscles

The skeletal muscles of the head and neck can be grouped on the basis of function, innervation, and embryological derivation.

In the head

The muscle groups in the head include:

the extra-ocular muscles (move the eyeball and open the upper eyelid),

muscles of the middle ear (adjust the movement of the middle ear bones),

muscles of facial expression (move the face),

muscles of mastication (move the jaw—temporomandibular joint),

muscles of the soft palate (elevate and depress the palate), and

muscles of the tongue (move and change the contour of the tongue).

In the neck

In the neck, major muscle groups include:

muscles of the pharynx (constrict and elevate the pharynx),

muscles of the larynx (adjust the dimensions of the air pathway),

strap muscles (position the larynx and hyoid bone in the neck),

muscles of the outer cervical collar (move the head and upper limb), and

postural muscles in the muscular compartment of the neck (position the neck and head).

Relationship to other regions

Thorax

The superior thoracic aperture (thoracic inlet) opens directly into the base of the neck (Fig. 8.11). Structures passing between the head and thorax pass up and down through the superior thoracic aperture and the visceral compartment of the neck. At the base of the neck, the trachea is immediately anterior to the esophagus, which is directly anterior to the vertebral column. There are major veins, arteries, and nerves anterior and lateral to the trachea.

Fig. 8.11 Superior thoracic aperture and axillary inlets.

Upper limbs

There is an axillary inlet (gateway to the upper limb) on each side of the superior thoracic aperture at the base of the neck (Fig. 8.11):

Structures such as blood vessels pass over rib I when passing between the axillary inlet and thorax.

Cervical components of the brachial plexus pass directly from the neck through the axillary inlets to enter the upper limb.

Key features

Vertebral levels CIII/IV and CV/VI

In the neck, the two important vertebral levels (Fig. 8.12) are:

Fig. 8.12 Important vertebral levels—CIII/CIV and CV/CVI.

between CIII and CIV, at approximately the superior border of the thyroid cartilage of the larynx (which can be palpated) and where the major artery on each side of the neck (the common carotid artery) bifurcates into internal and external carotid arteries; and

between CV and CVI, which marks the lower limit of the pharynx and larynx, and the superior limit of the trachea and esophagus—the indentation between the cricoid cartilage of the larynx and the first tracheal ring can be palpated.

The internal carotid artery has no branches in the neck and ascends into the skull to supply much of the brain. It also supplies the eye and orbit. Other regions of the head and neck are supplied by branches of the external carotid artery.

Airway in the neck

The larynx (Fig. 8.13) and the trachea are anterior to the digestive tract in the neck, and can be accessed directly when upper parts of the system are blocked. A cricothyrotomy makes use of the easiest route of access through the cricothyroid ligament (cricovocal membrane, cricothyroid membrane) between the cricoid and thyroid cartilages of the larynx. The ligament can be palpated in the midline, and usually there are only small blood vessels, connective tissue, and skin (though occasionally, a small lobe of the thyroid gland—pyramidal lobe) overlying it. At a lower level, the airway can be accessed surgically through the anterior wall of the trachea by tracheostomy. This route of entry is complicated because large veins and part of the thyroid gland overlie this region.

Fig. 8.13 Larynx and associated structures in the neck.

Cranial nerves

There are twelve pairs of cranial nerves and their defining feature is that they exit the cranial cavity through foramina or fissures.

All cranial nerves innervate structures in the head or neck. In addition, the vagus nerve [X] descends through the neck and into the thorax and abdomen where it innervates viscera.

Parasympathetic fibers in the head are carried out of the brain as part of four cranial nerves—the oculomotor nerve [III], the facial nerve [VII], the glossopharyngeal nerve [IX], and the vagus nerve [X] (Fig. 8.14). Parasympathetic fibers in the oculomotor nerve [III], the facial nerve [VII], and the glossopharyngeal nerve [IX] destined for target tissues in the head leave these nerves, and are distributed with branches of the trigeminal nerve [V].

Fig. 8.14 Cranial nerves and parasympathetic innervation.

The vagus nerve [X] leaves the head and neck to deliver parasympathetic fibers to the thoracic and abdominal viscera.

Cervical nerves

There are eight cervical nerves (C1 to C8):

C1 to C7 emerge from the vertebral canal above their respective vertebrae.

C8 emerges between vertebrae CVII and TI (Fig. 8.15A).

Fig. 8.15 Cervical nerves. A. Structure. B. Dermatomes.

The anterior rami of C1 to C4 form the cervical plexus. The major branches from this plexus supply the strap muscles, the diaphragm (phrenic nerve), skin on the anterior and lateral parts of the neck, skin on the upper anterior thoracic wall, and skin on the inferior parts of the head (Fig. 8.15B).

The anterior rami of C5 to C8, together with a large component of the anterior ramus of T1, form the brachial plexus, which innervates the upper limb.

Functional separation of the digestive and respiratory passages

The pharynx is a common chamber for the digestive and respiratory tracts. Consequently, breathing can take place through the mouth as well as through the nose, and material from the oral cavity can potentially enter either the esophagus or the larynx. Importantly:

The lower airway can be accessed through the oral cavity by intubation.

The digestive tract (esophagus) can be accessed through the nasal cavity by feeding tubes.

Normally, the soft palate, epiglottis, and soft tissue structures within the larynx act as valves to prevent food and liquid from entering lower parts of the respiratory tract (Fig. 8.16A).

Fig. 8.16 Larynx, soft palate, epiglottis, and oropharyngeal isthmus. A. Overall design. B. Normal breathing. C. Breathing with food or liquid in the oral cavity. D. Swallowing. E. In a newborn child.

During normal breathing, the airway is open and air passes freely through the nasal cavities (or oral cavity), pharynx, larynx, and trachea (Fig. 8.16A). The lumen of the esophagus is normally closed because, unlike the airway, it has no skeletal support structures to hold it open.

When the oral cavity is full of liquid or food, the soft palate is swung down (depressed) to close the oropharyngeal isthmus, thereby allowing manipulation of food and fluid in the oral cavity while breathing (Fig. 8.16C).

When swallowing, the soft palate and parts of the larynx act as valves to ensure proper movement of food from the oral cavity into the esophagus (Fig. 8.16D).

The soft palate elevates to open the oropharyngeal isthmus while at the same time sealing off the nasal part of the pharynx from the oral part. This prevents food and fluid from moving upward into the nasopharynx and nasal cavities.

The epiglottis of the larynx closes the laryngeal inlet and much of the laryngeal cavity becomes occluded by opposition of the vocal folds and soft tissue folds superior to them. In addition, the larynx is pulled up and forward to facilitate the moving of food and fluid over and around the closed larynx and into the esophagus.

In newborns, the larynx is high in the neck and the epiglottis is above the level of the soft palate (Fig. 8.16E). Babies can therefore suckle and breathe at the same time. Liquid flows around the larynx without any danger of entering the airway. During the second year of life, the larynx descends into the low cervical position characteristic of adults.

Triangles of the neck

The two muscles (trapezius and sternocleidomastoid) that form part of the outer cervical collar divide the neck into anterior and posterior triangles on each side (Fig. 8.17).

Fig. 8.17 Anterior and posterior triangles of neck.

The boundaries of each anterior triangle are:

the median vertical line of the neck,

the inferior margin of the mandible, and

the anterior margin of the sternocleidomastoid muscle.

The posterior triangle is bounded by:

the middle one-third of the clavicle,

the anterior margin of the trapezius, and

the posterior margin of the sternocleidomastoid.

Major structures that pass between the head and thorax can be accessed through the anterior triangle.

The posterior triangle in part lies over the axillary inlet, and is associated with structures (nerves and vessels) that pass into and out of the upper limb.

Regional anatomy

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 and 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. 8.18).

Frontal bone

The forehead consists of the frontal bone, which also forms the superior part of the rim of each orbit (Fig. 8.18).

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 foramen	Nasopalatine nerve; sphenopalatine vessels
Greater palatine foramen	Greater palatine nerve and vessels
Lesser palatine foramen	Lesser palatine nerves 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).

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.

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 the maxilla.

On the anterior surface of the body of the 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. It consists of the body of the mandible anteriorly and the ramus of the mandible posteriorly. These meet posteriorly at the angle of the mandible. All these parts of the mandible are visible, to some extent, in the anterior view.

The body of the mandible is arbitrarily divided into two parts:

The lower part is the base of the mandible.

The upper part is the alveolar part of the mandible.

The alveolar part of the mandible contains the teeth and is resorbed when the teeth are removed. The base of the 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 (Table 8.1) is visible halfway between the upper border of the alveolar part of the mandible and the lower border of the base of the mandible. Continuing past this foramen is a ridge (the oblique line) passing from the front of the ramus onto the body of the 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. 8.19):

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.

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. 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 the sphenoid bone (Fig. 8.19), 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. 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.

Temporal bone

A major contributor to the lower portion of the lateral wall of the cranium is the temporal bone (Fig. 8.19), 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. 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. 8.19) 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; 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 the mandible, a posterior ramus of the mandible, and the angle of the mandible where the inferior margin of the mandible meets the posterior margin of the ramus (Fig. 8.19).

The teeth are in the alveolar part of the body of the 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 condylar and coronoid processes 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.

Posterior view

The occipital, parietal, and temporal bones are seen in the posterior view of the skull.

Occipital bone

Centrally the flat or squamous part of the occipital bone is the main structure in this view of the skull (Fig. 8.20). 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.