Infratemporal fossa
This is a space lying beneath the base of the skull between the side wall of the pharynx and the ramus of the mandible. It is also referred to as the parapharyngeal or lateral pharyngeal space.
Boundaries
Its medial boundary is the lateral surface of the lateral pterygoid plate with, behind it, the tensor palati muscle and the superior constrictor. In front of the lateral pterygoid plate, between it and the maxilla, is the pterygo-maxillary fissure through which the infratemporal fossa communicates with the pterygopalatine fossa (see p. 369). The lateral wall is the ramus of the mandible and its coronoid process. The anterior wall is the posterior surface of the maxilla, at the upper margin of which is a gap between it and the greater wing of sphenoid—the inferior orbital fissure. The roof of the fossa is formed medially by the infratemporal surface of the greater wing of the sphenoid (perforated by the foramen ovale and foramen spinosum) and the adjacent squamous part of the temporal bone in front of the articular eminence (Fig. 6.19). This infratemporal surface of the sphenoid is bounded laterally by the infratemporal crest, where the bone takes an almost right-angled turn upwards to become part of the side of the skull, deep to the zygomatic arch and part of the temporal fossa. Thus the roof of the infratemporal fossa lateral to the infratemporal crest is not bony, but is the space deep to the zygomatic arch where the temporal and infratemporal fossae communicate. The posterior boundary is the styloid process with the carotid sheath behind it.
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Figure 6.19 Right infratemporal and palatal regions of the base of the skull. The petrosquamous and petrotympanic fissures lie in front of and behind the tegmen tympani. |
Contents
The fossa contains the deep part of the parotid gland, the medial and lateral pterygoid muscles, the insertion of temporalis into the coronoid process, the maxillary artery and its branches, the pterygoid venous plexus, the mandibular nerve and its branches together with the otic ganglion, the chorda tympani, and the posterior superior alveolar branches of the maxillary nerve.
Lateral pterygoid
This muscle arises by two heads: the upper from the roof of the infratemporal fossa and the lower from the lateral surface of the lateral pterygoid plate. The two heads, lying edge to edge, converge and fuse into a short thick tendon that is inserted into the pterygoid fovea on the front of the neck of the mandible. The upper fibres of the tendon pass back into the capsule and the articular disc of the temporomandibular joint (Fig. 6.20).
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Figure 6.20 Left pterygoid muscles and related structures. |
Nerve supply. By a branch from the anterior division of the mandibular nerve.
Action. When the muscle contracts it draws condyle and disc forwards from the mandibular fossa down the slope of the articular eminence (Fig. 6.35). It is indis-pensable to active opening of the mouth. It participates with medial pterygoid in chewing movements.
Medial pterygoid
This muscle also arises by two heads. The larger deep head arises from the medial (deep) surface of the lateral pterygoid plate. The muscle diverges down from the lateral pterygoid muscle at nearly a right angle from their common origin on either side of the lateral pterygoid plate (Fig. 6.20). A small slip of muscle, the superficial head, arises from the tuberosity of the maxilla and the pyramidal process of the palatine bone which insinuates itself between the tuberosity and the lower end of the lateral pterygoid plate (Fig. 6.13). Passing over the lower margin of the lateral pterygoid muscle, the superficial head fuses with the main muscle mass. In this way the two heads, very unequal in size, embrace the lower edge of the lateral pterygoid. The muscle passes down and back at 45°, and laterally to reach the angle of the mandible. It is inserted into the rough area on the medial surface of the angle as far as the groove for the mylohyoid vessels and nerve (see Fig. 8.5B, p. 510). The muscle is characterized by tendinous intersections on its surface, which account for the roughness of the area of insertion on the mandible.
Nerve supply. By a branch from the main trunk of the mandibular nerve (Fig. 6.21).
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Figure 6.21 Right otic and pterygopalatine ganglia and their connections and branches: medial aspect. Branches of the mandibular nerve and maxillary artery (first part) are also displayed. The upper part of the perpendicular plate of the palatine bone has been removed to reveal the pterygopalatine fossa. |
Action. The pull of the muscle on the angle of the mandible is upwards, forwards and medially (i.e. it closes the mouth) and it moves the mandible towards the opposite side in chewing. Contracting with its opposite fellow and the two lateral pterygoids, it helps to protrude the mandible.
Maxillary artery
The maxillary artery is, with the superficial temporal artery, a terminal division of the external carotid. It enters the infratemporal fossa by passing forwards deep to the neck of the mandible, between the neck and the sphenomandibular ligament. Here the auriculotemporal nerve lies above it (Fig. 6.21), and the maxillary vein below it. It usually runs deep (sometimes superficial) to the lower head and passes forward and upward between the two heads of the lateral pterygoid muscle (Fig. 6.20). It then passes deeply into the pterygomaxillary fissure and so into the pterygopalatine fossa.
It is described conventionally in three parts, before, on and beyond the lateral pterygoid muscle and this is useful, since five branches come from each part. From first and third parts the five branches all enter foramina in bones, from the second part the branches are mainly muscular.
The five branches from the first part are the inferior alveolar, middle meningeal, accessory meningeal and two branches to the ear.
The inferior alveolar artery passes downwards and forwards (vein behind it) towards the inferior alveolar nerve and all three enter the mandibular foramen. It passes forwards in the mandible, supplying the pulps of the mandibular molar and premolar teeth and the body of the mandible. Its mental branch emerges from the mental foramen and supplies the nearby lip and skin.
The middle meningeal artery passes vertically upwards to the foramen spinosum. It is embraced by the two roots of the auriculotemporal nerve (Fig. 6.21). Its course and distribution are described on page 442. From the sympathetic plexus on the artery a branch enters the otic ganglion.
The accessory meningeal artery passes upwards through the foramen ovale and supplies the dura mater of the floor of the middle fossa and of the trigeminal (Meckel's) cave. It is the chief source of blood supply to the trigeminal ganglion.
The remaining two arteries pass upwards to enter the ear and run superficial and deep to the tympanic membrane. The deep auricular artery is the more superficial of the two and supplies the external acoustic meatus, passing between the cartilage and bone. The deeper is the anterior tympanic artery which passes through the petrotympanic fissure to the middle ear to join the circular anastomosis around the tympanic membrane.
The second part of the maxillary artery gives off branches to the pterygoid muscles and masseter, and deep temporal branches to temporalis which ascend between the muscle and the temporal fossa. A small branch accompanies the buccal nerve.
The third part of the maxillary artery, in the pterygopalatine fossa, gives five branches (see below) which accompany branches of the maxillary nerve and the pterygopalatine ganglion (see p. 370). The artery then passes forwards, with the maxillary nerve, through the inferior orbital fissure into the orbit as the small infraorbital artery, which continues along the floor of the orbit and infraorbital canal to emerge with the infraorbital nerve on the face; its middle (occasional) and anterior superior alveolar branches supply maxillary incisor and canine teeth.
The sphenopalatine artery passes through the sphenopalatine foramen to enter the nasal cavity as its main artery of supply (see p. 374). The posterior superior alveolar artery gives branches that accompany the corresponding nerves through foramina in the posterior wall of the maxilla. The greater palatine artery gives off lesser palatine branches to the soft palate and passes through the greater palatine foramen to supply the hard palate (see p. 380). The very small pharyngeal artery enters the palatovaginal canal, and the artery of the pterygoid canal runs into its own canal.
The posterior superior alveolar nerve is a branch of the maxillary, given off in the pterygopalatine fossa and soon dividing into two or three branches which pierce the posterior wall of the maxilla separately. They are distributed to the molar teeth and the mucous membrane of the maxillary sinus. Another branch does not pierce the bone but runs along the alveolar margin of the maxilla as far forward as the first molar tooth, to supply the gingiva of the vestibule alongside the molar teeth. The posterior superior alveolar nerves can be blocked here by an injection through the vestibule of the mouth; on account of the proximity of the posterior superior alveolar vessels and the pterygoid venous plexus, a haematoma of some size may be a complication.
The pterygoid plexus is a network of very small veins that lie around and within the lateral pterygoid muscle. The veins draining into the pterygoid plexus correspond with the branches of the maxillary artery, but they do not return all the arterial blood, much of which returns from the periphery of the area by other routes (facial veins, pharyngeal veins, diploic veins). On the other hand the pterygoid plexus receives the drainage of the inferior ophthalmic vein(see p. 403), via the inferior orbital fissure, and the deep facial vein. The pterygoid plexus drains into a short maxillary vein which lies deep to the neck of the mandible. It runs back to join the superficial temporal vein and form the retromandibular vein. The plexus is valved and acts as a ‘peripheral heart’, aiding venous return by the pumping action of the lateral pterygoid muscle. Emissary veins connect the pterygoid plexus with the cavernous sinus through the foramen ovale and the foramen lacerum.
The sphenomandibular ligament is a flat band of tough fibrous tissue extending from a narrow attachment on the spine of the sphenoid. It broadens as it passes downwards to be attached to the lingula and inferior margin of the mandibular foramen (see Fig. 8.5B, p. 510). It is derived from the perichondrium of Meckel's cartilage (see Fig. 1.20, p. 25). Between it and the neck of the mandible pass the auriculotemporal nerve and the maxillary artery and vein. Between it and the ramus of the mandible the inferior alveolar vessels and nerve converge to the mandibular foramen. Any remaining space between the ligament and the mandible is occupied by parotid gland tissue. The ligament is pierced by the mylohyoid nerve, a branch from the inferior alveolar nerve, and the accompanying small mylohyoid artery and vein.
Mandibular nerve
The mandibular branch from the trigeminal ganglion lies in the dura mater of the middle cranial fossa lateral to the cavernous sinus. With the motor root of the trigeminal nerve it enters the foramen ovale, where the two join and emerge as the mandibular nerve (like spinal nerve roots in intervertebral foramina). The nerve lies deep to the upper (infratemporal) head of the lateral pterygoid, between it and the tensor palati muscle, with the otic ganglion applied to the deep surface of the nerve (Fig. 6.21). This point is 4cm deep to the articular tubercle on the zygomatic arch, when accessed through the mandibular notch. After a short course the nerve divides into a small anterior (mainly motor) and a large posterior (mainly sensory) branch.
Branches from the main trunk
One sensory and one motor. The meningeal branch, or nervus spinosus, re-enters the middle cranial fossa via the foramen spinosum, or the foramen ovale, supplying the meninges of the middle cranial fossa, and the mastoid air cells.
The nerve to the medial pterygoid runs forwards to the muscle, and gives a branch which passes through the otic ganglion without synapse to supply the two tensor muscles, tensor palati and tensor tympani.
Branches from the anterior division
This division is motor, except for one branch (the buccal nerve).
Two deep temporal branches to temporalis pass above the upper border of the lateral pterygoid muscle; one may be a branch of the buccal nerve.
The masseteric nerve, passing above the upper border of the lateral pterygoid, emerges through the mandibular notch to enter the deep surface of the masseter. It gives an articular branch to the temporomandibular joint.
The nerve to the lateral pterygoid runs with the buccal nerve and supplies both heads of the muscle.
The buccal nerve contains all the fibres of common sensation in the anterior division of the mandibular nerve. It emerges between the two heads of the lateral pterygoid (Fig. 6.20) and courses downwards and forwards on the buccinator, giving branches to the skin over the cheek. It then pierces the buccinator (giving proprioceptive fibres to it) and supplies the mucous membrane of the cheek and the gum of the lower jaw opposite the lower molars and second premolar (i.e. up to the mental foramen).
Branches from the posterior division
This division is sensory except for the motor fibres which are distributed via the mylohyoid nerve. There are three branches.
The auriculotemporal nerve is derived by two roots from the posterior division; they embrace the middle meningeal artery (Fig. 6.21). The nerve passes backwards between the neck of the mandible and the sphenomandibular ligament, lying above the maxillary vessels. It gives a branch to the temporomandibular joint, and ascends over the lateral aspect of the zygomatic arch behind the superficial temporal vessels (Fig. 6.11). The auricular part innervates the skin of the tragus and upper part of the lateral surface of the pinna, the external acoustic meatus and the outer surface of the tympanic membrane. The temporal part is distributed to the skin of the temple. The auriculotemporal nerve is in contact with the anteromedial surface of the parotid gland, and supplies it with postganglionic secretomotor fibres from the otic ganglion.
The inferior alveolar (dental) nerve emerges below the lower head of the lateral pterygoid and curves down on the medial pterygoid (Fig. 6.20). The nerve lies anterior to its vessels between the sphenomandibular ligament and the ramus of the mandible, and enters the mandibular foramen. It is into this region, just above the foramen, that anaesthetic solution is introduced for inferior alveolar nerve block (see p. 379). The inferior alveolar nerve lies midway between the anterior and posterior borders of the mandibular ramus at the level of the midpoint of the posterior border of the ramus. The mylohyoid nerve leaves the inferior alveolar at the foramen. It pierces the sphenomandibular ligament and lies on a groove on the mandible in front of the insertion of the medial pterygoid (see Fig. 8.5B, p. 510), accompanied by small branches of the inferior alveolar artery and vein. The mylohyoid nerve then runs forward on the superficial (cervical) surface of the mylohyoid supplying it and the anterior belly of the digastric (Fig. 6.6); the nerve often carries sensory fibres from a small area of submental skin and may participate in the sensory supply to lower incisors.
The inferior alveolar nerve runs with its vessels in the mandibular canal. It supplies the three molar and two premolar teeth. Then it divides into the mental nerve (see p. 354) and the incisive nerve. The latter nerve supplies the canine and both incisors, with some overlap into the opposite central incisor.
The lingual nerve appears below the lateral pterygoid and passes forwards and downwards on the medial pterygoid (Fig. 6.20). It then comes into contact with the mandible, where the bone is thinned to form a shallow groove below and medial to the third molar, just above the posterior end of the mylohyoid line (see Fig. 8.5B, p. 510). This groove separates the attachments of the pterygomandibular raphe above and mylohyoid muscle below (Fig. 6.22). The nerve is characteristically flattened here, rather than round, and it enters the mouth on the superior surface of the mylohyoid. It gives off a gingival branch which supplies all the lingual gum and mucous membrane of the floor of the mouth. The lingual nerve then crosses the submandibular duct (see p. 338) and runs forwards and medially to the tongue.
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Figure 6.22 Course of the right lingual nerve from outside the pharynx to within the mouth. In A, viewed from within the mouth, the nerve is seen passing under the free lower border of the superior constrictor, which interdigitates with buccinator at the pterygomandibular raphe. In B, the nerve is viewed from above, entering the mouth in contact with the periosteum below and behind the third molar tooth. |
The chorda tympani (from the facial nerve, see p. 417) emerges through the petrotympanic fissure (Fig. 6.35), grooves the medial surface of the spine of the sphenoid, and joins the lingual nerve at an acute angle (Fig. 6.21), 2cm below the base of the skull, and is distributed with it to the anterior two-thirds of the tongue. It carries parasympathetic secretomotor fibres to the submandibular ganglion and taste fibres from the anterior two-thirds of the tongue (see p. 382).
Otic ganglion
This small body lies between the tensor palati and the mandibular nerve, just below the foramen ovale. It is a flat plaque, about 2–3mm in diameter, closely applied to the medial surface of the nerve (Fig. 6.21). It is a relay station for parasympathetic secretomotor fibres to the parotid gland; the lesser petrosal branch of the glossopharyngeal nerve brings these fibres. Postganglionic sympathetic fibres from the plexus around the middle meningeal artery, sensory fibres from the auriculotemporal nerve and a branch from the nerve to the medial pterygoid (to tensor tympani and palati) pass through the ganglion without relay. The connections of the otic ganglion are summarised on page 22.
Carotid sheath and cranial nerves
Carotid sheath
The carotid sheath extends from the base of the skull to the arch of the aorta. In its upper part it is attached to the margins of the carotid canal and the jugular fossa. It contains here the internal carotid artery and internal jugular vein (see p. 343) and the last four (ninth to twelfth) cranial nerves. Medial to it lies the pharynx; laterally the deepest part of the parotid gland touches the sheath, partly separated by the styloid process and its three muscles. Anteriorly is the infratemporal fossa. Behind the carotid sheath lies the cervical sympathetic trunk on the prevertebral fascia.
The carotid canal lies immediately in front of the jugular foramen (which lies deep to the external acoustic meatus). The internal jugular vein lies behind the internal carotid artery at the base of the skull, but slopes as it descends, and at a lower level lies lateral to the common carotid artery as the vessels lie on scalenus anterior. At all levels the vagus nerve lies deep in the groove between the two, within the carotid sheath. The glossopharyngeal and accessory nerves emerge at the base of the skull between artery and vein and immediately curve away from each other superficial to the vessels (Fig. 6.23). The hypoglossal nerve emerges from the hypoglossal canal medial to the sheath. It passes through the sheath behind the inferior vagal ganglion and turns forwards to emerge between the artery and vein.
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Figure 6.23 Right internal jugular vein, carotid arteries and related cranial nerves. |
Glossopharyngeal nerve
The glossopharyngeal nerve emerges from the anterior part of the jugular foramen on the lateral side of the inferior petrosal sinus (see p. 447). It makes a deep notch in the inferior border of the petrous bone and here its inferior ganglion bulges the nerve. The ganglion contains the cell bodies of most sensory fibres in the nerve. The nerve passes down on the lateral aspect of the internal carotid artery and curves forward around the lateral side of stylopharyngeus (Figs 6.23 and 6.41). It passes deep to the external carotid artery and continues forward deep to hyoglossus to reach the tongue (see p. 382).
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Figure 6.41 Pharynx from behind with the nasopharynx opened to show the soft palate musculature: A is a probe entering the opening of the auditory tube; B is a probe passed down between middle and inferior constrictors, emerging through Killian's dehiscence. The diagram is based on a prosection in the Anatomy Museum of the Royal College of Surgeons of England. |
The tympanic branch (Jacobson's nerve) leaves the nerve at the jugular fossa and passes through a canaliculus on the ridge of petrous bone between the carotid and jugular foramina (Fig. 6.19) to enter the temporal bone and supply the middle ear, mastoid air cells and bony part of the auditory tube with sensory fibres. In this branch are also parasympathetic fibres from the inferior salivary nucleus. They run through the tympanic plexus on the promontory and continue in the lesser petrosal nerve. This nerve leaves the middle ear through its roof and runs along the floor of the middle cranial fossa to the foramen ovale, through which it passes to reach the otic ganglion (Fig. 6.27). The parasympathetic fibres relay in the otic ganglion for the secretomotor supply of the parotid gland and the other small glands of the vestibule of the mouth.
The motor branch to stylopharyngeus is given off as the nerve spirals around the posterior border of that muscle.
The carotid sinus nerve is the main supply to the carotid sinus and carotid body (baroreceptors and chemoreceptors.
One or more pharyngeal branches join the pharyngeal plexus on the middle constrictor muscle (see p. 386). They pierce the muscle and supply the mucous membrane of the oropharynx with common sensation and (a few) taste fibres.
The tonsillar branch supplies the mucous membrane over most of the (palatine) tonsil.
The lingual branch supplies the posterior one-third of the tongue with sensory fibres (common sensation and taste) and secretomotor fibres to the glands of the posterior third. These last relay in small ganglia in the mucous membrane.
Vagus nerve
The vagus nerve emerges through the middle compartment of the jugular foramen, in which a small enlargement constitutes the superior ganglion. Just below the base of the skull the elongated inferior ganglion dilates the trunk. The ganglia contain cell bodies of the afferent fibres of the vagus; the superior ganglion for the meningeal and auricular branches, the inferior ganglion for all the other sensory fibres. Just above the inferior ganglion the vagus is joined by a large branch from the accessory nerve (cranial part), comprising nucleus ambiguus fibres for the skeletal muscle of the soft palate, pharynx and larynx.
The nerve runs straight down the neck, within the carotid sheath, between and behind carotid (internal and common) artery and jugular vein. In the root of the neck it passes in front of the subclavian artery and so enters the mediastinum (see p. 196) to supply thoracic and abdominal viscera.
Meningeal branches pass up from the superior ganglion to supply the dura mater of the posterior fossa below the tentorium.
The auricular branch (Arnold's nerve) runs laterally through a canaliculus in the lateral wall of the jugular fossa. It supplies the posteroinferior quadrant of the outer surface of the tympanic membrane and a small adjacent area of skin of the external acoustic meatus and a little area of skin on the cranial auricular surface.
The very fine carotid body branch forms a plexus with the carotid sinus branch of the glossopharyngeal for the supply of those structures.
The pharyngeal branch of the vagus passes forward between the internal and external carotid arteries (Fig. 6.23) and joins the pharyngeal plexus on the middle constrictor muscle. The fibres supply the muscles of the pharynx (except stylopharyngeus) and the muscles of the soft palate (except tensor palati, see p. 390).
The superior laryngeal nerve slopes downwards on the side wall of the pharynx deep to the internal carotid artery (Fig. 6.23). It divides into a large internal laryngeal nerve which pierces the thyrohyoid membrane to reach the piriform recess (see p. 388), carrying sensory fibres for the pharynx and larynx, and a small external laryngeal nerve which runs down close to the superior thyroid vessels, outside the larynx, to supply cricothyroid and contribute to the supply of the inferior constrictor.
The cervical cardiac branches are two on each side. They all pass down to the deep part of the cardiac plexus (see p. 194), except for the lower left branch which goes to the superficial part of the plexus.
The recurrent laryngeal nerve on the right hooks around the subclavian artery at the root of the neck (Fig. 6.9). On the left side the recurrent laryngeal nerve is given off in the superior mediastinum and recurves around the ligamentum arteriosum under the arch of the aorta (see Fig. 4.13, p. 192). Both nerves then ascend along the posterolateral border of the trachea, in a groove between it and the oesophagus, and pass under the lower border of the inferior constrictor. Both nerves have cardiac branches, and also supply the trachea, oesophagus and the cricopharyngeus part of the inferior constrictor, before entering the pharynx and larynx to supply the laryngeal muscles (except cricothyroid) and the laryngeal mucosa from the vocal folds downwards (see p. 396).
Accessory nerve
The accessory nerve is formed in the posterior cranial fossa by union of cranial and spinal (cervical) roots. The nerve occupies the middle compartment in the jugular foramen, just lateral to the vagus, with which it shares a meningeal sleeve. All the fibres of its cranial root leave the nerve in a branch which joins the vagus. The nerve, now consisting of cervical fibres only, runs downwards and backwards on the internal jugular vein (Fig. 6.23), where the latter lies on the transverse process of the atlas; the nerve crosses lateral (usually) or medial to the vein. It passes deep to the styloid process and posterior belly of the digastric, where it is crossed by the occipital artery. With the upper sternocleidomastoid branch of the occipital artery it reaches the sternocleidomastoid, supplies it and enters its deep surface. Emerging from the posterior border of the muscle it crosses the posterior triangle (see p. 333) to supply trapezius.
Hypoglossal nerve
The hypoglossal nerve emerges from the hypoglossal canal. It picks up a branch from the anterior ramus of C1 and then spirals behind the inferior ganglion of the vagus to emerge between the internal carotid artery and internal jugular vein, passing through the carotid sheath. It then descends on the carotid sheath, deep to the styloid muscles and the posterior belly of digastric. It is crossed by the occipital artery and its lower sternocleidomastoid branch and then turns forwards, superficial to both carotid arteries and the loop of the lingual artery (Fig. 6.23), just above the tip of the greater horn of the hyoid bone. It continues forwards on the hyoglossus (Fig. 6.24), accompanied by veins draining the tip of the tongue, to supply tongue muscles.
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Figure 6.24 Right styloid process and submandibular region. The right half of the mandible and part of the submandibular and sublingual glands have been removed. The glossopharyngeal nerve, stylohyoid ligament and lingual artery pass deep to the posterior border of hyoglossus; the lingual nerve, submandibular duct and hypoglossal nerve are superficial to hyoglossus. |
The C1 fibres that join the hypoglossal nerve leave it progressively in the superior root of the ansa cervicalis and in the branches to thyrohyoid and geniohyoid. The small meningeal branch which enters the posterior fossa through the hypoglossal canal also comprises C1 fibres.
Styloid apparatus
The styloid process is a part of the temporal bone. From its tip the stylohyoid ligament passes to the lesser horn of the hyoid bone (Fig. 6.24). Both process and ligament are remnants of the second pharyngeal arch cartilage (see Fig. 1.21, p. 25). Hence the styloid process is very variable in length, the ligament varying likewise, inversely with it.
Three muscles diverge from the styloid process and are described elsewhere. The stylopharyngeus (see p. 386) arises highest from the medial side of the base of the process and passes downwards to the larynx. The stylohyoid (see p. 335) arises from the posterior surface near the base, and the styloglossus (see p. 381) from in front low down and from the upper end of the stylohyoid ligament; they diverge as they pass downwards and forwards to the hyoid bone and side of the tongue respectively. Each of the three muscles has a different nerve supply. They all act significantly during swallowing.
The styloid apparatus (process and muscles) lies lateral to the carotid sheath. The external carotid artery passes between the muscles of the stylohyoid apparatus. It runs up deep to digastric and stylohyoid, but superficial to stylopharyngeus (Fig. 6.23), to enter the parotid gland. The retromandibular vein, on the other hand, passes down from the parotid gland superficial to stylohyoid and digastric.
