Department of Anatomy

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Human Anatomy

Head and Neck

FOR MEDICAL AND DENTAL STUDENTS

Revised by: Dr. Nikravesh

page 31:

CRANIAL CAVITY

Objectives:

1. Describe the reflections of the dura mater with special reference to the

formation of the dural folds (falx cerebri, falx cerebelli, tentorium

cerebelli and diaphragma sellae).

2. Identify the major divisions of the forebrain, midbrain, and hindbrain.

3. Identify the twelve cranial nerves as they emerge from the brain and as

they pass out of the skull.

4. Describe the formation and course of the dural venous sinuses.

5. Describe the walls and lining of a typical dural venous sinus.

6. Describe the contents of the cavernous sinus.

7. Name the vessels that drain into the cavernous sinus.

8. Describe the general arrangement of the three cranial fossae and

enumerate the structures transmitted through the foramina in each fossa.

9. Discuss the anatomical basis of the signs and symptoms of fractures

involving the anterior, middle or posterior cranial fossa.

10. What are the possible sequelae of a fracture of:

(a) the cribriform plate of the ethmoid bone?

(b) the squamous portion of the temporal bone?

11. Outline the nerve supply and blood supply of the dura mater.

12. Discuss the clinical importance of the middle meningeal artery and its

branches.

13. Describe the course of the internal carotid artery from the carotid canal

to the base of the brain.

QUESTIONS FOR STUDY:

1. Into what major vein do the dural venous sinuses drain?

2. What is the difference between a diploic vein, an emissary vein and a

dural venous sinus?

3. What arteries and nerves supply the meninges surrounding the brain?

4. What is the confluence of the sinuses?

5. By what pathway could (a) an infection on the skin of the cheek pass

to the cavernous sinus; and (b) an infection travelling in the retromandibular

vein pass to the cavernous sinus?

6. What might be one of the earliest symptoms of cavernous sinus

thrombosis? Why?

7. How does cerebrospinal fluid drain into the venous system?

page 32:

ORBIT AND LACRIMAL APPARATUS

Relevant skeletal features:

bony orbit - axis;

medial wall - frontal process of the maxilla; lacrimal; orbital plate

of the ethmoid; body of the sphenoid;

floor - zygomatic; maxilla; orbital process of the palatine;

lateral wall - zygomatic; greater wing of the sphenoid;

roof - orbital plate of the frontal; lesser wing of the

sphenoid;

openings - optic canal; superior orbital fissure; inferior orbital

fissure; infraorbital foramen; supraorbital notch or

foramen; nasolacrimal canal; anterior ethmoidal

foramen; posterior ethmoidal foramen.

Fossa for lacrimal gland.

Fascial sheath of eyeball:

check ligaments; suspensory ligament.

Extraocular muscles:

levator palpebrae superioris; superior rectus; inferior rectus; medial

rectus; lateral rectus; superior oblique; inferior oblique.

Nerves:

optic; ophthalmic division of trigeminal (lacrimal, frontal, nasociliary

branches); oculomotor; trochlear; abducent; zygomatic; infraorbital.

Ciliary ganglion.

Arteries:

ophthalmic artery and its branches.

Veins:

superior and inferior ophthalmic.

Lacrimal apparatus:

lacrimal gland; lacrimal ducts; conjunctival sac; lacrimal papilla; lacrimal

punctum; lacrimal canaliculus; lacrimal sac; nasolacrimal duct.

page 33:

ORBIT AND LACRIMAL APPARATUS DISSECTION

1. With a skull for reference, note that the orbit lies below the anterior cranial

fossa and in front of the middle cranial fossa. Now proceed as follows:

(a) remove the superior wall of the orbit and the supraorbital margin

by making two sagittal sawcuts through the frontal bone above

the medial and lateral ends of the orbital margin;

(b) carefully remove the supraorbital margin and the orbital plate of

the frontal bone with bone forceps so as to expose the orbital

periosteum. Take care not to damage the underlying nerves.

Remove the bone back to and including the lesser wing of the

sphenoid bone and in this way open the superior orbital fissure

and optic canal; and

See if there is an extension of the frontal sinus into the orbital plate.

2. Remove the orbital periosteum taking care not to damage the nerves

which lie immediately beneath it. Identify and clean:

(a) the frontal nerve, a branch of the ophthalmic division, lying on

the levator palpebrae superioris muscle in the middle of the

orbit. Trace this nerve forwards where it divides into supraorbital

and supratrochlear branches which have already been noted in

the scalp;

page 34:

(b) the trochlear nerve running along the medial side of the orbit to

supply the superior oblique muscle of the eyeball on its superior

aspect;

along the lateral aspect of the orbit.

3. Clean the levator palpebrae superioris and superior rectus muscles.

The latter muscle lies deep to the levator. Secure the upper division of

the oculomotor nerve supplying these muscles on their ocular surface.

4. Clean the superior oblique muscle situated on the medial side of the

orbit. Note that its tendon passes through a pulley near the superomedial

angle of the orbit, where it turns backwards to pass deep to the levator

palpebrae superioris and superior rectus to be inserted into the sclera

of the eyeball.

5. Divide the levator palpebrae superioris and the superior rectus about

their middle sparing the overlying frontal nerve. Trace the optic nerve

and the ophthalmic artery. The artery crosses the optic nerve superiorly

from the lateral to the medial side.

6. Identify the nasociliary branch of the ophthalmic division of the

trigeminal nerve which also crosses the optic nerve superficially from

the lateral to the medial side, after which it runs between the superior

oblique and medial rectus muscles. Clean this nerve and trace its

branches:

(a) a slender twig to the ciliary ganglion. Make use of this slender

twig to try to identify the ciliary ganglion which lies lateral to the

optic nerve at the apex of the orbit. It is of the size of a pin head;

(b) two long ciliary nerves which pass along with the optic nerve to

pierce the sclera;

the posterior and anterior ethmoidal foramina; and

(d) the infratrochlear nerve passing towards the medial angle of the

eye where it supplies the root of the nose and the medial part of

the upper eyelid.

7. Trace the short ciliary nerves from the ciliary ganglion. These run

above and below the optic nerve towards the eyeball.

8. Clean and trace the branches of the ophthalmic artery, most of which

are named according to the nerves which they accompany. Secure the

central artery of the retina, the most important branch of the

ophthalmic artery. It enters the optic nerve on its inferior surface. Note

that it is an end artery.

9. Secure the abducent nerve running along the ocular surface of the

lateral rectus to supply it.

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10. Identify the medial rectus muscle, which lies below the superior oblique,

and trace its nerve supply from the lower division of the oculomotor nerve.

11. Cut the optic nerve and turn the eyeball forwards to see the inferior

rectus muscle. Secure the nerve supply to this muscle from the lower

division of the oculomotor nerve. Trace a twig from the branch to the

inferior oblique towards the ciliary ganglion.

12. Observe the origin of the recti from the common tendinous ring, which

extends between the medial side of the optic canal and the spicule of

bone on the inferior margin of the superior orbital fissure. Note the

oblique direction of the superior and inferior recti in relation to the

axis of the eyeball. Check the insertions of the recti which are attached

to the sclera in front of the equator. Note that the medial and lateral

recti are anchored to their respective walls of the orbit by fascial

thickenings called check ligaments.

13. Observe the origins of the superior oblique and levator palpebrae

superioris from the sphenoid medial to and above the optic canal

respectively. Follow the tendon of the superior oblique to its insertion

into the sclera in the upper lateral quadrant of the eyeball behind the equator.

14. Cut horizontally through the lower eyelid near its margin and lift the

eyeball. Note the origin of the inferior oblique from the floor of the

orbit just lateral to the nasolacrimal canal. Note that the muscle passes

below the inferior rectus to reach its insertion on to the sclera behind

the equator in the lower lateral quadrant of the eyeball. Trace the nerve

supply to this muscle from the inferior division of the oculomotor nerve,

which enters it on its posterior border.

15. Look for the lacrimal gland in the upper lateral part of the orbit where it

causes a bulge in the conjunctiva. Carefully incise the upper eyelid along

the superior orbital margin and divide the conjunctiva at the superior

conjunctival fornix. With care remove the conjunctiva and examine the

gland. Note that some fibres of the levator palpebrae superioris are attached

to the conjunctiva. Trace the remaining part of the muscle into the tarsal

plate, the fascia and the skin of the upper eye lid.

16. Examine the medial and lateral palpebral ligaments, which attach

the medial and lateral extremities of the upper and lower tarsal plates

to the respective orbital margins.

17. Dissect carefully in the medial angle of the eye and identify the lacrimal

sac lying in a depression called the lacrimal fossa on the medial wall

of the orbit.

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18. Define the attachment of the lacrimal part of the orbicularis oculi

muscle to the posterior margin of the lacrimal fossa.

19. Remove the eyeball on one side and strip the periosteum off the floor

of the orbit. Note the infraorbital nerve and artery lying in the infraorbital canal.

Summary

The fascial sheath covering the eyeball, known as the fascia bulbi, extends

up to the sclerocorneal junction. This fascial sheath is prolonged along

the tendons to surround the muscle bellies of the recti.

From the lateral and medial recti, fascial extensions are attached to the

adjacent parts of the orbit giving rise to the check ligaments which prevent

undue backward displacement and compression of the eyeball. Between

these check ligaments, the inferior part of the fascial covering of the eyeball

is thickened so that it suspends the eyeball like a hammock. This is known

as the suspensory ligament. Thus the eyeball does not rest on the floor of the orbit.

All the extraocular muscles are supplied by the oculomotor nerve, except

the superior oblique which is supplied by the trochlear nerve and the lateral

rectus which is supplied by the abducens nerve (LR6 SO4)3.

The action of the extraocular muscles are complicated. They provide the

finer adjustments of the eyeball for visual activity, whereas coarse

adjustments are produced by reflex movements of the head and neck in the

required direction.

In the neutral position with the visual axis directed forwards, the medial

and lateral recti produce direct medial and lateral movements of the eyeball.

The superior and inferior recti are, however, not simple elevators and

depressors only. They cross the equator from the back to the front and their

direction is oblique since they travel forwards and laterally. Hence both

superior and inferior recti also cause medial deviation of the globe. The

superior and inferior oblique muscles cross the equator from the front to

the back and their direction is also oblique since they travel backwards and

laterally. Their oblique pull thus causes a lateral deviation in addition to

their actions of depression and elevation respectively. Hence, in the normal

movements, it is said that the superior rectus acts in concert with the inferior

oblique muscle of the same eye to produce the desired movement of pure

elevation, while the inferior rectus in combination with superior oblique

produces pure depression.

The structures passing through the superior orbital fissure deserve

attention as this fissure is the passageway for a large number of structures

entering or leaving the orbit. The fissure is divided by the common tendinous

ring into three parts. The part above and lateral to the ring transmits the

lacrimal, frontal and trochlear nerves and the superior ophthalmic vein.

Within the ring and between the two heads of the lateral rectus pass the two

divisions of the oculomotor nerve, and the nasociliary and abducent nerves.

Below the ring lies the inferior ophthalmic vein.

The ciliary ganglion is a relay station for parasympathetic fibres reaching

the ganglion via the oculomotor nerve. From the ganglion, the short ciliary

nerves run forwards to supply the ciliary muscle concerned with

accommodation and the sphincter pupillae muscle which constricts the pupil.

The lacrimal gland receives its secretomotor fibres from the

pterygopalatine ganglion which receives preganglionic fibres via the

greater petrosal branch of the facial nerve.

page 37:

ORBIT AND LACRIMAL APPARATUS

Objectives:

1. Describe the constitution of the four walls of the bony orbit.

2. Describe the arrangement of orbital fat and orbital fascia.

3. Describe the origins and insertions of the extraocular muscles.

4. Define the visual axis and illustrate the actions of these muscles.

5. Summarise the sensory and motor nerves in the orbit and deduce the

effects of lesions of the third, fourth and sixth cranial nerves both alone

and in combination.

6. Discuss the clinical importance of:

(a) the venous drainage of the orbit; and

(b) the central artery of the retina.

7. Identify, on a living subject, the surface anatomy features of the eye,

eyelids, and lacrimal apparatus.

8. Describe the lacrimal apparatus, including the mechanisms by which

tears are produced and drained via the puncta, lacrimal canaliculi,

lacrimal sac and nasolacrimal duct.

9. Give an account of the distribution and function of each major branch

of the ophthalmic division of the trigeminal nerve.

QUESTIONS FOR STUDY:

1. Where would one find the superior tarsal muscle? What is its function?

What is its innervation?

2. What structures pass through (a) the superior orbital fissure; and

(b) the optic foramen?

3. How would you test for integrity of the trochlear nerve and the abducent

nerve?

page 38:

THE EYE

Relevant features:

outer coat - cornea, sclera;

middle coat - choroid, ciliary body;

ciliary muscle and its nerve supply;

iris, its muscles and their nerve supply;

inner coat - retina and its parts;

arterial supply - central artery of the retina;

anterior chamber;

posterior chamber;

lens;

aqueous humor;

vitreous body.

THE EYEBALL

You will be unable to obtain a clear idea of the internal structure of the

eyeball from the eyes of the cadaver you are dissecting. You should

therefore examine the fresh eyeball of an ox.

Dissection of the eyeball of an ox

1. Make also full use of demonstration material.

2. Students should work in pairs and each group should be provided with

two ox eyes.

3. Remove the muscles, fat, fascia, and conjunctiva from the ox’s eyeball

with which you have been provided. This is best done with a pair of

scissors, starting behind where the optic nerve pierces the outer coat

of the eyeball (the sclera), and working forwards and round the globe.

4. The centre of the cornea in front is called the anterior pole of the

eyeball; the corresponding point at the back of the eyeball is the

posterior pole; the line joining the poles coincides with the optic axis

of the eyeball.

5. One eye should be divided sagittally and the other equatorially (frontal).

Examine the sections, and notice that there are three coats:

(a) an outer protective, formed by the sclera or “white” of the eye in

the posterior five-sixths, and the transparent cornea in the anterior sixth;

(b) an intermediate vascular and pigmented coat, the choroid,

continued anteriorly into the ciliary body and iris; and

so thin that it tears with the slightest touch, and will be found to be

opaque and wrinkled from the action of preservative agents.

These three coats enclose three refractive media, they are the aqueous

humour, the lens and the vitreous body, from before backwards.

Now examine these features more closely:

page 39:

1. The sclera is reinforced posteriorly by the sheath of the optic nerve

and joins anteriorly with the cornea at the corneoscleral junction.

2. The cornea is thicker near the corneoscleral junction than at the

anterior pole of the eye. Both parts of the outer coat are made of

fibrous tissue, but in front all the component elements of this tissue

have the same refractive index, and so the cornea is transparent. The

cornea is covered in front with a layer of stratified epithelium directly

continuous with the conjunctiva.

3. If the corneoscleral junction is examined carefully with a hand-lens,

the small venous sinus of the sclera (canal of Schlemm) will be seen

cut in section. This venous sinus drains excess aqueous humour from

the anterior chamber of the eye (see below).

4. The choroid coat is continued forwards into the iris and is pigmented.

Posteriorly it is perforated by the optic nerve, while anteriorly, just

before it joins the iris, it becomes folded to form the ciliary body, to

be noted later. It is essentially a vascular coat.

5. The iris is the diaphragm which, by varying the size of its opening, the

pupil can regulate the amount of light admitted to the eye. It lies very

close to and just in front of the lens, although there is a small triangular

space known as the posterior chamber of the eye between the two

which is bounded peripherally by the bases of the ciliary processes. It

is thus seen that only the pupillary margin of the iris is in contact with

the lens capsule. The anterior chamber of the eye lies between the

cornea and the iris, and is about 3 mm from before backwards. These

two chambers contain the aqueous humor.

6. The retina is seen as a delicate, whitish membrane, which easily

separates from the choroid, especially when the vitreous humour is

removed. A similar “detachment of the retina” sometimes occurs in

life as the result of a blow on the eye. Note that the whole of the retina

is not present in the delicate white membrane, which is the true nervous

layer, pars optica retinae, because there is a layer of cells containing

a black pigment, which developmentally belongs to the retina but is

left behind on the choroid when the retina separates from it. This

pigmented layer, lined internally by columnar epithelium, is continued

forward over the inner surface of the ciliary processes, and here the

epithelial cells play an important part in the secretion of the aqueous

humour; this part of the retina is known as the pars ciliaris retinae.

On the back of the iris too, the black pigment layer, together with the

columnar cells, here also pigmented, is very marked and is called the

pars iridica retinae. Where the inner nervous layer of the retina ends,

i.e. at the junction of the pars optica and pars ciliaris retinae, it presents

a scalloped edge, the ora serrata.

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7. The lens in the dissecting laboratory is opaque, especially if it has

been treated with spirit. It is enclosed in a structure-less capsule but

this is not visible to the naked eye. In section it is biconvex, with the

anterior surface a good deal flatter than the posterior. It is about 8mm

in diameter. The vitreous body fills the cavity of the eyeball behind

the lens; it has consistency of a very thin jelly and is enclosed by a

delicate membrane called the hyaloid membrane. Extending from the

back of the ciliary body to the margin of the lens all round its

circumference is a membrane formed of fine radiating fibres, which

splits to enclose the lens. The anterior is the stronger of the two layers

formed by the splitting and passes in front of the lens to blend with its

capsule. This is known as the suspensory ligament of the lens and

when the ciliary processes are drawn forward, it relaxes and allows the

front of the lens to become more convex through its own elasticity.

The posterior layer of the splitting continues to enclose the vitreous

body and lies in close contact with the back of the lens. Running right

through the vitreous body, from the entrance of the optic nerve to the

middle of the back of the lens, is the hyaloid canal. In the fetus, this

canal transmits a branch from the retinal artery to the back of the lens.

8. Now take the posterior half of the eyeball which was divided

transversely, and scoop out the vitreous body as gently and carefully

as possible. It will retain its shape if it is placed in a vessel of water,

because of the hyaloid membrane and a minute and very delicate

network in its interior. On examining the retina, preferably with a

magnifying lens, the optic disc will be seen opposite the point where

the optic nerve enters (3 mm to the medial or nasal side of the posterior

pole of the eye). It is a circular disc only 1.5mm across, and in its

centre is the place where the retinal artery breaks up into radiating

branches supplying the retina. The variations in the appearance of the

disc are of great clinical importance, and may be examined with an

ophthalmoscope in the living subject. The optic disc, which consists

only of nerve fibres, corresponds to the “blind spot” of the eye.

9. Having removed the vitreous body from the eyeball, note that there is

no macula lutea (yellow spot) in the ox, since this only occurs in

animals which use their eyes for binocular vision. On the other hand,

an iridescent colouring, not found in humans, is present in the eye of

the ox. This is caused by a layer of fine connective tissue fibres on the

inner aspect of the choroid, known as the tapetum. It is more

particularly observed in nocturnal animals, especially the carnivores,

and is the cause of the glare seen in the eye of a cat or dog, for example, in the dark.

10. In the anterior half of the eye, remove the vitreous humour and trace

the retina forward. As already noted, a little behind the region of the

ciliary body its nervous elements end in the scalloped edge called the

ora serrata, though a pigmented and epithelial layer is continued

forwards as the pars ciliaris and pars iridica retinae over the back of

the ciliary processes and iris.

11. Carefully remove the lens. The ciliary body can now be seen from

behind. The pigment of the retina that covers it makes it look black.

12. The ciliary processes form a delicate fringe of vascular glomeruli which

is present on the convex surface of the ciliary body.

page 41:

13. Next cut through the cornea close to the corneoscleral junction threequarters

of the way round, and open it like a lid. Lining the back of the

cornea is the posterior limiting membrane, which may be peeled

away from the cut edge slightly, and is continued onto the front of the

iris as a series of delicate ridges with spaces in between. This is the

pectinate ligament, and the spaces are the spaces of the iridocorneal

angle (filtration angle). It is here that the aqueous humour, secreted at

the surface of the ciliary body, percolates into the adjacent venous sinus

of the sclera.

14. The iris can now be seen from the front and back. Behind, the iris has

the black pigment of the pars iridica retinae, but seen from the front its

colour may range from dark brown to light blue, according to the amount

of interstitial pigment which is deposited in the stroma of the iris. The

iris contains circular (sphincter pupillae muscle) and radiating (dilator

pupillae muscle) muscular fibres, but they are impossible to

demonstrate macroscopically.

15. Lastly, in the ox eye, which was bisected sagitally, examine the cut

surface carefully with a hand-lens to see the ciliary muscle rising from

the corneoscleral junction, close to the venous sinus of the sclera, and

running backwards into the ciliary body in a fan-like manner. Internal

to these are some circular fibres, but it is very difficult to make them

out without a microscope.

Summary

The eye is a highly specialised sense organ designed to transmit visual

stimuli to the brain. An optical system of transparent refracting media brings

images of external objects to focus on a complex light-sensitive membrane,

called the retina, at the back of the eyeball. From here nerve fibres pass to

the brain through the optic nerve, conveying information about the images

that have been received. Other parts of the eye are responsible for the

focussing of the optical system, and for controlling the amount of light

falling on the retina.

Note that:

(a) The ciliary muscle is supplied by preganglionic fibres from the

oculomotor nerve which relay in the ciliary ganglion and continue as

postganglionic parasympathetic fibres in the short ciliary nerves. The

muscle draws the choroid forwards and slackens the suspensory

ligament of the lens so that the lens can become more convex in

accommodating for near vision.

(b) The sphincter pupillae muscle is supplied by preganglionic fibres

from the oculomotor nerve which relay in the ciliary ganglion and

continue as postganglionic parasympathetic fibres in the short ciliary

nerves. The muscle contracts the pupil.

the first thoracic segment of the spinal cord which relay in the superior

cervical ganglion and continue as postganglionic sympathetic fibres

in the long ciliary nerves. This muscle is responsible for pupil

enlargement.

page 42:

THE EYE

Objectives:

1. Describe the layers of the eye.

2. Describe the smooth muscles in the eye and their innervation.

3. Describe the circulation of the aqueous humor.

4. What is the importance of the central artery of the retina?

QUESTIONS FOR STUDY:

1. What is the difference between the orbital axis and the visual (optic)

axis? How does this difference affect the way in which the individual

extraocular muscles are tested?

2. What is diplopia?

3. What are the major features of the following reflexes:

(a) the light reflex;

(b) the accommodation reflex; and

4. What is glaucoma?

5. What is cataract?

PAROTID AND INFRATEMPORAL REGIONS AND TEMPOROMANDIBULAR JOINT:

Parotid and Infratemporal Regions

Relevant skeletal features:

mandible - body; mylohyoid line and groove; mental foramen;

angle; ramus; condylar process (head); neck;

pterygoid fovea; coronoid process; mandibular

notch; lingula; mandibular foramen;

temporal bone - squamous part; tympanic plate; styloid

process; zygomatic process; external acoustic

meatus; mastoid process; stylomastoid foramen;

squamotympanic and petrotympanic fissures;

mandibular fossa; articular tubercle;

sphenoid bone - greater wing; infratemporal crest; lateral and medial

pterygoid plates; scaphoid fossa; spine; foramen

ovale; foramen spinosum;

maxilla - tuberosity; posterior surface.

pterygomaxillary fissure; pterygopalatine fossa.

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Deep fascia:

capsule of parotid gland.

Ligaments:

stylomandibular; sphenomandibular.

Parotid gland:

surfaces and relations; duct; facial nerve and branches; retromandibular

vein; external carotid artery; lymph nodes; nerve supply of the gland.

Muscles:

masseter; temporalis; medial and lateral pterygoids.

Nerves:

mandibular and branches; chorda tympani; maxillary and branches; facial

and branches.

Arteries:

external carotid; superficial temporal; maxillary artery and branches.

Veins:

retromandibular; pterygoid plexus.

Temporomandibular Joint

Muscles in relation to capsule:

lateral pterygoid.

Capsule:

attachments.

Ligaments:

lateral ligament.

Accessory ligaments:

sphenomandibular; stylomandibular.

Intra-articular structures:

articular disc.

Synovial membrane:

reflection.

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Movements:

protraction; retraction; elevation; depression; side to side movements.

Nerve supply:

auriculotemporal; masseteric.

Blood supply:

PAROTID AND INFRATEMPORAL REGIONS DISSECTION:

1. Remove the superficial layer of the deep cervical fascia covering the

parotid gland. Note that the gland lies below the zygomatic arch, in

front of the mastoid process and sternocleidomastoid muscle, and

behind the ramus of the mandible which it overlaps. Observe that a

portion of the gland tissue lies above the parotid duct over the surface

of the masseter muscle. This is the accessory parotid gland. Trace

the duct forwards and note that it pierces the buccinator muscle to

open into the vestibule of the mouth opposite the crown of the upper

second molar tooth.

2. Try to look for lymph nodes on the superficial surface of the gland.

3. Carefully remove the substance of the gland piecemeal and trace the

following structures from superficial to deep:

(a) the branches of the facial nerve proximally to the parent trunk.

Note that there are communications between the branches of the

facial, auriculotemporal and great auricular nerves;

(b) the retromandibular vein formed by the union of the superficial

temporal and maxillary veins; and

superficial temporal and maxillary branches at the level of the

neck of the mandible.

4. Remove the remains of the gland and study its deep relations formed

by the styloid process, tympanic plate and posterior belly of the

digastric muscle. Note that the space occupied by the gland is wedge

shaped and consequently the gland has lateral, anteromedial and

posteromedial surfaces. It also has an upper and lower pole. Observe

the stylomandibular ligament extending between the styloid process

and the angle of the mandible and forming the lower limit of the

gland.

5. Clean the masseter muscle arising from the zygomatic arch and gaining

insertion into the outer surface of the ramus of the mandible. Note the

direction of the muscle fibres. Cut the zygomatic arch at its root and

anteriorly through the temporal process of the zygomatic bone using

a saw and bone forceps. Reflect the cut arch and attached masseter

muscle downwards. Note the mandibular notch.

6. Trace the insertion of the temporalis muscle into the coronoid process.

7. Cut the coronoid process along with the insertion of the temporalis

and reflect the muscle upwards. Note the deep temporal vessels and

nerves running deep to the muscle. Observe that the anterior fibres of

the muscle are vertical while the posterior fibres are almost horizontal.

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Superficial dissection of infratemporal fossa

8. Remove the ramus of the mandible by two saw cuts, one through the

neck of the mandible and the other, a shallow cut, obliquely across

the body just anterior to the angle of the mandible. Carefully nibble

away the bone between the two cuts with bone forceps so as to expose

the contents of the mandibular canal. Remove the fragments of the

ramus and thereby gain access to the infratemporal region.

9. Identify and carefully clean the following branches of the mandibular

division of the trigeminal nerve:

(a) the inferior alveolar nerve entering the mandibular foramen

together with the inferior alveolar vessels. Note that the nerve

appears below the lower border of the lateral pterygoid muscle

and passes downwards, and that it gives off the mylohyoid nerve

posteriorly which pierces the sphenomandibular ligament;

(b) the lingual nerve, also emerging below the lower border of the

lateral pterygoid in front of the inferior alveolar nerve and running

downwards and forwards on the medial pterygoid muscle; and

pterygoid muscle and running forwards to pierce the buccinator.

It supplies the mucous membrane of the cheek.

10. Clean the pterygoid muscles and study their attachments. Observe the

origin of the upper head of the lateral pterygoid muscle from the

roof of the infratemporal fossa and the lower head from the lateral

surface of the lateral pterygoid plate. Trace the fibres of the muscle

backwards to their insertion into the front of the neck of the mandible.

The additional insertion of this muscle into the capsule and articular

disc of the temporomandibular joint will be seen later.

11. Now clean the large deep head of the medial pterygoid muscle arising

from the medial surface of the lateral pterygoid plate and the smaller

superficial head from the tuberosity of the maxilla. Follow the muscle

downwards, backwards and laterally to its insertion into the medial

surface of the angle of the mandible and the adjoining area.

12. Identify the maxillary artery and note that its course is divided into

three parts by the lateral pterygoid muscle. The second part of the artery

may pass either deep or superficial to this muscle.

13. On one side carefully remove the lateral pterygoid muscle, leaving

behind a small portion of the muscle close to its insertion into the neck

of the mandible.

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14. Clean the maxillary artery. In its first part it gives off several branches

of which the main ones are:

(a) the middle meningeal artery entering the middle cranial fossa

through the foramen spinosum. Note that the artery ascends

between the two roots of the auriculotemporal nerve;

(b) the inferior alveolar artery entering the mandibular foramen in

company with the inferior alveolar nerve after giving off the

mylohyoid branch. In the mandibular canal, the nerve supplies

branches to the mandible and all the lower teeth. Its terminal part,

the mental nerve, passes through the mental foramen and has

already been seen; and

The first part of the maxillary artery lies deep to the neck of the

mandible. The second part, associated with the lateral pterygoid muscle,

supplies the masseter, temporalis, pterygoid, and buccinator muscles,

and the third part of the artery enters the pterygopalatine fossa.

15. Note that the veins accompanying the branches of the maxillary artery

form a plexus known as the pterygoid plexus. The plexus

communicates with the cavernous sinus mainly through the

foramen ovale and foramen lacerum. It also communicates with the facial vein.

Temporomandibular Joint

16. Examine the temporomandibular joint on the same side where the

lateral pterygoid has been removed. As you proceed with your

dissection, again verify the attachment of the tendon of the lateral

pterygoid to the neck of the mandible; the capsule and articular disc.

Clean the fibrous capsule and note that it has a thickened lateral

ligament which stretches downwards and backwards between the

zygoma and the neck of the mandible.

17. Open the joint cavity by cutting across the joint capsule and observe

that it is subdivided into two parts by means of an articular disc, which

is concavoconvex above to adapt to the mandibular fossa situated in

the squamous part of the temporal bone. Note that the articular disc

is attached anteriorly and posteriorly to the capsule and to the medial

and lateral sides of the head of the mandible. Now remove the head of

the mandible.

18. Trace the auriculotemporal nerve from behind the joint to its origin

from the mandibular nerve and note that it splits around the middle

meningeal artery.

19. Trace the chorda tympani nerve, a branch of the facial nerve, emerging

from the petrotympanic fissure and joining the lingual nerve on its

upper posterior aspect.

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20. Note that the following additional branches are given off from the trunk

of the mandibular division of the trigeminal nerve:

(a) a meningeal branch which enters the cranial cavity through the foramen spinosum; and

(b) the nerve to the medial pterygoid.

Deep dissection of infratemporal fossa

21. Clean the lateral surface of the lateral pterygoid plate on the same

side where the lateral pterygoid muscle had previously been removed.

Next remove the lateral plate and the medial pterygoid muscle with

bone foreceps. Cut the lingual and inferior alveolar nerves close to

their origin and reflect the mandibular nerve trunk and try to find the

otic ganglion which lies on the medial side of the mandibular nerve

trunk. Carefully clean the exposed area.

22. Now identify the triangular tensor veli palatini muscle which is

attached to the base of the skull and lies on the side of the pharynx

medial to the medial pterygoid muscle. The tensor veli palatini is

supplied by the mandibular nerve.

23. Follow the maxillary artery towards the pterygomaxillary fissure

where it enters the pterygopalatine fossa (the third part of the artery)

to break up into the infraorbital, posterior superior alveolar, and

branches supplying the pharynx, palate, nose, etc. Note that the

infraorbital artery enters the orbit through the inferior orbital fissure

together with the infraorbital nerve. The posterior superior alveolar

branches enter the posterior surface of the maxilla along with the

posterior superior alveolar branches of the maxillary nerve.

24. Try to identify the maxillary nerve in the upper part of the

pterygomaxillary fissure and trace its infraorbital and superior alveolar

branches which accompany the corresponding branches of the maxillary artery.

Summary

In the parotid region, the most important structure is the facial nerve which

passes through the substance of the parotid gland. As the nerve lies superficial

to the blood vessels, the nerve can be damaged before any serious bleeding

is noticed during parotid surgery. Injury to the facial nerve produces a

condition known as facial palsy, which results in flaccid paralysis of the

facial muscles. In this condition, the patient is unable to close the eyes and

there is drooping of the angle of the mouth with dripping of saliva.

The muscles of mastication produce movements of the mandible and are

consequently attached to this bone. Note that the pterygoids, temporalis

and masseter, which are the muscles of mastication, are all attached to the

ramus of the mandible. The medial and lateral pterygoid muscles which

cause side to side movement of the lower jaw have a lateral inclination

while passing from their origin to their insertion on to the mandible. Thus,

the pterygoids of one side are able to protrude the lower jaw and rotate the

chin to the opposite side. The attachment of the tendon of the lateral

pterygoid to the articular disc and neck of the mandible ensures that the

articular disc is also drawn forward, as the jaw is protracted by the contraction

of this muscle so that the condyle can rest within the concavity of the disc.

It must also be noted that both temporomandibular joints act in unison,

i.e. they act as a single joint.

All muscles of mastication are developed from the first branchial arch

and are therefore supplied by the mandibular nerve which is the nerve of

the first arch. The mandibular nerve, after its exit through the foramen ovale,

divides into anterior and posterior divisions. The branches of the anterior

division are all motor except for the buccal branch, which is sensory, while

the branches of the posterior division are all sensory, except for the

mylohyoid nerve, which supplies the mylohyoid and the anterior belly of

the digastric muscle.

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PAROTID GLAND

Objectives:

1. Define the surfaces of the gland and parotid ‘bed’.

2. Describe the relations of the gland.

3. Describe the fascial relation of the gland.

4. Enumerate the structures inside the gland from superficial to deep,

stressing the importance of this arrangement in parotid surgery.

INFRATEMPORAL REGION AND TEMPOROMANDIBULAR JOINT

Objectives:

1. Compare the formation of the mandibular nerve trunk to that of a mixed spinal nerve.

2. Enumerate the branches from the trunk and divisions of the mandibular nerve.

3. Enumerate the main branches of the first two parts of the maxillary artery.

4. Analyse the role of the pterygoid venous plexus in the spread of sepsis into the cranial cavity.

5. Define the articular surface of the condylar process of the mandible and the mandibular fossa.

6. Describe the capsule of the joint.

7. Ascribe the functional roles to:

(a) the articular disc and the reciprocally concavoconvex nature

of the articular surfaces; and

(b) the sphenomandibular and stylomandibular ligaments.

8. Deduce the line of pull of:

(a) the vertical and horizontal fibres of the temporalis; and

(b) the medial pterygoid, lateral pterygoid and masseter.

9. Define the muscles taking part in protraction, retraction, elevation,

depression and side to side movements of the mandible.

10. Discuss the functional significance of Hilton’s law as applied to the joint, with special reference to proprioception.

11. Describe the innervation of the teeth and gingivae.

12. Give an account of the chorda tympani.

13. Describe the innervation of the buccal mucosa and of the lower teeth.

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QUESTIONS FOR STUDY:

1. The parotid fascia is an upward continuation of what layer of deep

fascia in the neck?

2. Why are infections of the parotid gland, such as mumps, so painful?

What nerves are involved?

3. Why is the buccinator muscle referred to as an accessory muscle of

mastication? To what other important muscle does it attach?

4. What structures must be avoided during surgical dissection of the

parotid gland?

5. What is trismus?

6. During what movement is the mandible most easily dislocated?

7. Where would a dentist inject in order to anaesthetise the lower teeth?

8. What branch of the trigeminal nerve receives cutaneous sensation from

(a) the upper lip; (b) the dorsum of the nose; (c) the chin; and (d) the upper eyelid?

9. What branch of the trigeminal nerve supplies general sensory

innervation to: (a) the cornea; (b) the lower second molar tooth; (c) the

upper central incisor tooth; (d) the mucosa of the lateral wall of the

nose; and (e) the mucosal lining of the cheek?

10. What muscles are innervated by the motor root of the trigeminal nerve?

How can this nerve be tested?

11. What branch of the trigeminal nerve supplies the temporomandibular joint?

12. How could an infection involving the buccal pad of fat spread to the

cavernous sinus?

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SUBMANDIBULAR REGION AND DEEP DISSECTION OF THE NECK

Submandibular Region

1. Clean the two bellies of the digastric muscle and note that the

posterior belly arises from the mastoid notch of the temporal bone.

The origin of the anterior belly from the digastric fossa of the

mandible has already been noted. Follow the two bellies to their

intermediate tendon which is attached to the hyoid bone by a loop of

fibrous tissue. The nerve supply to the posterior belly comes from

the facial nerve and to the anterior belly from the mylohyoid branch

of the inferior alveolar nerve.

2. Clean the stylohyoid muscle, which arises from the styloid process

and runs along the upper border of the posterior belly of the digastric

to be inserted into the hyoid bone. The nerve supply to this muscle

comes from the facial nerve.

3. Detach the anterior belly of the digastric from its origin and clean the

mylohyoid muscle, which arises from the mylohyoid line of

the mandible and is inserted into a median raphe anteriorly and into

the hyoid bone. Observe that the muscle has a free posterior border. Its

nerve supply comes from the mylohyoid nerve.

4. Note that the facial vein is joined by the anterior branch of the

retromandibular vein and lies superficial to the submandibular

gland. The facial vein drains into the internal jugular vein.

5. Clean the submandibular gland and observe that the major (superficial)

part of the gland lies on the mylohyoid muscle while the deep portion

passes deep to the muscle by curving round its posterior border. Note

that the facial artery lies in a groove in the posterior part of the gland.

Trace the artery as it descends between the gland and the mandible to

appear at the anteroinferior angle of the masseter, where its pulsation

can be felt in the living.

6. Now displace the gland laterally and carefully cut and reflect the thin

mylohyoid muscle from the mandible to expose the hyoglossus and

the genioglossus muscles. Define the origin of the hyoglossus from

the greater horn of the body of the hyoid bone and its insertion into the

posterior part of the side of the tongue. Observe that the genioglossus

arises from the superior mental spine from where it fans out to be

inserted into the whole length of the tongue close to the midline. The

most inferior fibres are inserted into the hyoid bone. Below the

genioglossus, identify the geniohyoid muscle passing from the inferior

mental spine to the hyoid bone.

7. Clean the structures which lie on the hyoglossus muscle. These are

from above downwards:

(a) lingual nerve;

(b) submandibular ganglion suspended from the lingual nerve;

(d) hypoglossal nerve.

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Note that the deep part of the submandibular gland also lies on the

hyoglossus muscle. Trace the lingual nerve and note that it crosses the

submandibular duct superficially and then recrosses the duct on its

deep aspect further forwards.

8. Identify and trace the styloglossus muscle which takes origin from

near the tip of the styloid process and the stylohyoid ligament and

runs downwards and forwards to be inserted into the whole length of

the side of the tongue. The nerve supply to the styloglossus, hyoglossus

and genioglossus muscles comes from the hypoglossal nerve. C1 fibres

running along with the hypoglossal nerve supply the geniohyoid and

thyrohyoid muscles.

9. Carefully cut the hyoglossus from the hyoid bone, raise the muscle

upwards and trace the lingual artery. Note that the course of the lingual

artery is divided into three parts by the hyoglossus muscle. After giving

off the dorsal lingual branches, the artery continues as the deep artery

of the tongue. Identify the middle constrictor muscle of the pharynx

on which the proximal part of the lingual artery lies.

10. Observe that the facial artery lies first on the middle constrictor and

then on the superior constrictor muscle of the pharynx where it

gives off its tonsillar branch before reaching the posterior part of the

submandibular gland.

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