1. INFRATEMPORAL FOSSAE; TMJ
Steven J. Zehren, Ph.D.
TEMPORAL &
INFRATEMPORAL FOSSAE; TMJ

2. OSTEOLOGY

3. BOUNDARIES OF TEMPORAL FOSSA
Greater wing
of sphenoid
Superior temporal line
Squamous temporal
Parietal
Pterion
Zygomatic arch
Frontal
The temporal fossa is on the side of the cranium. Temporal derived from Latin tempus, time, and is used b/c gray hairs first appear here.
THE BOUNDARIES of the temporal fossa are the sup. temporal line above and the zygomatic arch below.
The FLOOR of the fossa is formed by the frontal (blue), parietal (green), gr. wing of the sphenoid (yellow) and squamous part of the temporal (red). The area where these four bones converge in an H-shaped suture is the pterion. The pterion is an imp. landmark --- it overlies a branch of the mid. meningeal a. on the inside of the skull.
The CONTENTS of the temporal fossa are the temporalis m. and its nerve and blood supply.
The ROOF of the temporal fossa is formed by temporal fascia. The fascia is a strong, glistening membrane which attaches to the sup. (?) temporal line above and to the zygomatic arch below.
The ANTERIOR WALL of the temporal fossa is formed by the zygomatic bone. This wall separates the temporal fossa from the orbit. The anterior wall is bony only in primates; it is membranous in animals like the dog.
Zygomatic bone

4. BOUNDARIES OF THE INFRATEMPORAL FOSSA --- I
Ramus of mandible
(lateral wall)
As the name suggests, the infratemporal fossa lies below the temporal fossa.
1. The ramus of the mandible forms the LATERAL WALL of the infratemporal fossa.

5. BOUNDARIES OF THE INFRATEMPORAL FOSSA --- II
Infratemporal crest of
greater wing of sphenoid
Infratemporal surface of
greater wing of sphenoid
(roof)
Infratemporal surface of
maxilla (anterior wall)
Orient. Mandible and zygomatic arch have been removed.
The ROOF OF THE INFRATEMPORAL FOSSA is formed by the infratemporal surface of the gr. wing of the sphenoid. The roof of the infratemporal fossa is separated from the temporal fossa by the infratemporal crest of the gr. wing of the sphenoid. The MEDIAL WALL OF THE FOSSA is the lat. pterygoid plate of the sphenoid . The ANTERIOR WALL is the infratemporal surface of the maxilla and the POSTERIOR WALL is the styloid pr. of the temporal bone.
Note the maxillary tuberosity --- a roughened area just posterosuperior to the third maxillary molar which serves for part of the origin of the med. pterygoid m.
Styloid process
(posterior wall)
Lateral pterygoid plate
(medial wall)
Maxillary tuberosity

6. COMMUNICATIONS OF INFRATEMPORAL FOSSA --- I
Inf. orbital fissure
(to orbit)
Pterygomaxillary fissure
(to pterygopalatine fossa)
The PTERYGOMAXILLARY FISSURE (appropriately named) forms a communication between the infratemporal fossa (laterally) and the pterygopalatine fossa (medially). It transmits the maxillary a.
The INF. ORBITAL FISSURE connects the infratemporal fossa with the orbit. It transmits the infraorbital vessels.
The PETROTYMPANIC FISSURE (appropriately named) forms a communication between the infratemporal fossa and the tympanic (middle ear) cavity. It transmits the chorda tympani n.
Petrotympanic fissure
(to tympanic cavity)

7. COMMUNICATIONS OF INFRATEMPORAL FOSSA --- II
F. ovale
(to middle cranial fossa)
F. spinosum
(to middle cranial fossa)
The roof of the infratemporal fossa has two imp. foramina. The F. OVALE transmits the mandibular n. (V3) and the lsr. petrosal n. (br. of IX) from the mid. cranial fossa to the infratemporal fossa. The F. SPINOSUM transmits the mid. meningeal a. into the mid. cranial fossa. Adjacent to the f. spinosum is the SPINE OF THE SPHENOID --- a little spicule of bone which serves for the attachment of the sphenomandibular ligament.
Spine of sphenoid

8. FEATURES OF MANDIBLE Condylar process Head Pterygoid fovea
Coronoid process
Neck
Mandibular notch
Lingula
Mylohyoid groove
Mandibular f.
Ramus
This slide shows some imp. features of the mandible which need to be considered when studying the infratemporal fossa.
The RAMUS OF THE MANDIBLE forms the lateral wall of the infratemporal fossa. The ramus ends superiorly in two processes: 1) the CORONOID PR. (for insertion of the temporalis m.) and 2) the CONDYLAR PR. (consisting of the head and neck). The PTERYGOID FOVEA is a depression on the ant. surface of the neck for insertion of part of the lat. pterygoid m. The coronoid and condylar prs. are separated by the MANDIBULAR NOTCH (INCISURE) which transmits the masseteric n. and vessels to the masseter m. On the med. surface of the ramus is the MANDIBULAR F., partially guarded by a small "tongue-like" process of bone (LINGULA). The mandibular f. leads into the bony mandibular canal and transmits the inf. alveolar n. and vessels. Just prior to entering the mandibular f. the inf. alveolar n. and vessels give off the nerve and vessels to the mylohyoid m.; these lie in the shallow MYLOHYOID GROOVE. The med. surface of the angle of the mandible is roughened --- this is the area for insertion of the med. pterygoid m.
The BODY OF THE MANDIBLE bears the mental f. below the 2nd premolar tooth for the passage of the mental n. and vessels.
Mental foramen
Angle
Body

9. MUSCLES OF
MASTICATION

10. TEMPORALIS & MASSETER MUSCLES
Temporalis fascia
Temporalis m.
Zygomatic arch
Deep part
(masseter m.)
Superficial part
(masseter m.)
There are four muscles of mastication. The TEMPORALIS is a large, fan-shaped muscle which fills the temporal fossa. It originates from the bones forming the floor of the temporal fossa as well as from the temporalis fascia covering the muscle. The tendon of the temporalis inserts into the coronoid pr. and ant. border of the ramus of the mandible. The ant. fibers of the temporalis run vertically so they close the jaw (elevate the mandible). The post. fibers run horizontally and function to retract the mandible.
2. The MASSETER M. consists of superficial and deep fibers. The superficial fibers arise from the zygomatic pr. of the maxilla and the lower border of the zygomatic arch. The deep fibers arise from the lower border and medial surface of the zygomatic arch. The insertion of the masseter is into the lateral surfaces of the coronoid pr., ramus and angle of the mandible. Since the deep fibers run vertically and the superficial fibers obliquely, the masseter not only elevates but also protracts the mandible.

11. TEMPORALIS & MASSETER MUSCLES
Insertion of temporalis m.
(into coronoid process)
In this plate the insertions of the temporalis and masseter are well displayed.
Note also the masseteric n. and a. passing through the mandibular notch to reach the deep surface of the muscle.
Masseteric n. & a.
Insertion of masseter m.
(into ramus)

12. LATERAL & MEDIAL PTERYGOID MUSCLES
Articular disc of TMJ
Superior and inferior heads
of lateral pterygoid m.
Superficial and deep heads
of medial pterygoid m.
Pterygoid fovea
of neck of mandble
The LAT. PTERYGOID M. has two heads. The UPPER HEAD originates from the infratemporal surface of the gr. wing of the sphenoid. It inserts into the articular disc (meniscus) of the TMJ. The LOWER HEAD (main part) originates from the lat. surface of the lat. pterygoid plate. It inserts into the pterygoid fovea of the neck of the mandible. The two heads of the lat. pterygoid protract the jaw (chief protractor). They also depress the jaw because as the head of the mandible is pulled forward it also moves downward below the articular tubercle.
The MED. PTERYGOID M. also has two heads. The DEEP HEAD (main part) arises from the med. surface of the lat. pterygoid plate. The SUPERFICIAL HEAD arises from the maxillary tuberosity. The two heads unite and have a common insertion into the med. surface of the angle and ramus of the mandible (as high as the mandibular f.). This muscle runs parallel to the superficial fibers of the masseter --- it therefore does the same thing, ie, elevates and protracts the jaw.
Angle of mandible

13. “SPHENOMENISCUS M.” Articular disc (meniscus) ANTERIOR
Because of its attachments the upper head of the lateral pterygoid m. is sometimes referred to as the SPHENOMENISCUS MUSCLE.

14. LATERAL & MEDIAL PTERYGOID MUSCLES (POSTERIOR VIEW)
Lateral pterygoid plate
Lateral pterygoid m.
An additional function of the med. and lat. pterygoid mm. can be understood by examining this post. view of the jaws. Note that the origins of both pterygoid mm. are more medial than their insertions. Thus, if the PTERYGOID MM. ON ONLY ONE SIDE CONTRACT THE MANDIBLE IS PULLED TO THE OPPOSITE SIDE (BLUE ARROW) (ie, they produce CONTRALATERAL MOVEMENT). Alternate contraction of the pterygoid mm. on the two sides produces side to side grinding movements.
Medial pterygoid m.

15. EFFECT OF MANDIBULAR N. (V3) LESION
All of the muscles of mastication are innervated by the mandibular n. (V3). A lesion of V3 will lead to atrophy of these muscles (note sunken “cheek”) and deviation of the jaw toward the side of the lesion (b/c of the unopposed pull of the healthy lateral pterygoid m. when opening the jaw).

16. NERVES

17. V. TRIGEMINAL N.
SKELETAL MOTOR --- TO MUSCLES OF MASTICATION , ETC. (ARCH 1)
GENERAL SENSORY-- FROM FACE, NASAL & ORAL CAVITIES, ETC.
V GANGLION
(general sensory)
OPHTHALMIC N. (VI)
(general sensory)
MAXILLARY N. (V2)
(general sensory)
1. V has three main branches or divisions: Ophthalmic (V1), maxillary (V2) and mandibular (V3).
2. V has two major functions:
a. Skeletal motor to the muscles of mastication, plus a few other muscles also derived from pharyngeal
arch 1.
b. General sensory fibers from the skin of the face, mucosa of the nasal and oral cavities and paranasal
sinuses, the teeth, etc. (V is chief general sensory n. of head).
3. All of the skeletal motor fibers in V travel in V3, but the general sensory fibers travel in all three branches. The
sensory fibers have their cell bodies in the V ganglion.
MANDIBULAR N. (V3)
(general sensory, skeletal motor)

18. PHARYNGEAL ARCHES IN 4-WEEK EMBRYO
Site of midbrain
Pharyngeal (branchial) arches
Lens placode
Somites 4 3 2 1
Nasal placode
The pharyngeal arches are bars of tissue that form in the walls of the pharynx during the 4th week.
Each arch gives rise to skeletal elements, muscles, vessels, and skin/mucosa in the adult.
Stomodeum
Heart A
Slide 10.1

19. PHARYNGEAL ARCH NERVES
MAXILLARY N. (V2)
MANDIBULAR N. (V3)
Each pharyngeal arch is associated with a cranial n. that innervates the tissues derived from that arch.
2. The trigeminal n. (V) is associated with pharyngeal arch I, which is divided into two processes: the maxillary process innervated by the maxillary n. (V2) and the mandibular process innervated by the mandibular n. (V3).
3. Since many of the tissues derived from the mandibular process are associated with the infratemporal fossa, it is logical that the mandibular n. is the chief nerve of this fossa.

20. MANDIBULAR NERVE (V3) Temporalis fascia and m.
Ant. division (V3) (mostly motor)
Posterior and
anterior deep temporal nn.
Post. division (V3) (mostly sensory)
Foramen ovale
Masseteric n.
Lateral pterygoid n.
and m.
Auriculotemporal n.
Chorda tympani n.
(br. of VII)
Buccal n.
Lingual n.
Inferior alveolar n. (cut)
The MANDIBULAR N. (V3) IS THE CHIEF NERVE OF THE INFRATEMPORAL FOSSA. V3 enters the infratemporal fossa through the f. ovale. The TRUNK OF V3 ALMOST IMMEDIATELY SPLITS INTO AN ANT. AND POST. DIVISION.
The ANT. DIVISION IS MOSTLY MOTOR. It gives off ANT. & POST. DEEP TEMPORAL NN. to the temporalis, the MASSETERIC N. and the N. TO THE LAT. PTERYGOID. THE ONLY PURELY SENSORY BRANCH of the ant. division is the BUCCAL N. It supplies the skin and mucosa of the cheek.
The POST. DIVISION IS MOSTLY SENSORY. It gives off the AURICULOTEMPORAL N. (sensory to parotid gl., TMJ, auricle and temple), LINGUAL N. (general sensory to ant. two-thirds of tongue and floor of mouth) and INF. ALVEOLAR N. (sensory to mandibular teeth and, via its mental br., chin and lower lip). The ONLY MOTOR BRANCH of the post. division is the MYLOHYOID N. which supplies not only that muscle but also the ant. belly of the digastric. (Note that both the lingual and inf. alveolar nn. cross superficial to the med. pterygoid m.)
Another imp. nerve in the infratemporal fossa is the CHORDA TYMPANI (VII). After emerging from the petrotympanic fissure it passes anteroinferiorly to join the lingual n. The chorda tympani contains two functional components: 1) SVA (for taste on the ant. two-thirds of the tongue) and 2) GVE (presynaptic parasympathetic fibers destined to synapse in the submandibular ganglion). Postsynaptic fibers then go to supply the submandibular and sublingual gls..
Mylohyoid n.
Mylohyoid m. (cut)
Submandibular ganglion
& gland
Mental n.
Sublingual gland
Inferior alveolar n. (cut)
Digastric m. (anterior belly)

21. MANDIBULAR NERVE (V3) (MEDIAL VIEW) Otic ganglion V3
Lesser petrosal n. (IX)
Facial n. (VII)
Tensor palatini n. & m.
Chorda tympani n.
Tympanic membrane
Medial pterygoid n. & m.
Tensor tympani n. & m.
Before dividing into ant. and post. divisions the TRUNK OF V3 gives off branches to several muscles. These include branches to the MEDIAL PTERYGOID M., the TENSOR (VELI) PALATINI M. and the TENSOR TYMPANI M. The tensor palatini is a muscle of the soft palate and the tensor tympani m. is associated with the middle ear.
The OTIC GANGLION is a tiny parasympathetic ganglion lying in the infratemporal fossa just medial to V3. Also shown is the lsr. petrosal n. (IX) carrying presynaptic parasympathetic fibers to the ganglion. Postsynaptic parasympathetic fibers are then distributed to the parotid gland via the auriculotemporal n.
Note the CHORDA TYPANI N. branching off of the facial n. and running across the medial surface of the tympanic membrane. After leaving the middle ear via the petrotympanic fissure it joins the lingual n. in the infratemporal fossa.
4. Note the MYLOHYOID N. splitting off from the inf. alveolar n. just superior to the mandibular f.
Auriculotemporal n.
Inf. alveolar n.
Mylohyoid n.
Lingual n.

22. CUTANEOUS BRANCHES OF V3
The three cutaneous (=supplies skin) branches of V3 are the mental n. (to skin of lower lip and chin), the buccal n. (to skin of cheek) and the auriculotemporal n. (to skin of auricle (ear) and temple).
These three branches supply a strip of skin (pink) referred to as the V3 dermatome. The V1 dermatome is shown in green and the V2 dermatome in blue. V3
dermatome
Mental n.
Buccal n.
Auriculotemporal n.

23. HERPES ZOSTER INFECTION (SHINGLES) Herpes Zoster (also called
Which branch
of what nerve?
-is considered a
latent response to a
chicken pox virus
located in the
trigeminal ganglion
Herpes zoster is a viral disease affecting nerve ganglia; it may be due to a reactivation of the chicken pox virus. In this case the virus has affected the trigeminal ganglion and its mandibular division (V3), resulting in the eruption of vesicles in the skin supplied by this nerve.

24. FACIAL NERVE BRANCHES IN PAROTID GLAND
Temporal branches
Zygomatic branches
THE FACIAL NERVE IS THE MOTOR NERVE OF THE FACE. The main trunk of VII emerges from the skull base and enters the parotid gland. Within the gland it divides into five terminal branches: 1) Temporal br. 2) Zygomatic br. 3) Buccal br. 4) Marginal mandibular br. and 5) Cervical br. (Mnemonic: "To Zanzibar By Motor Car“). These brs. fan out onto the face and innervate the muscles of facial expression, including the buccinator m. in the cheek.
 2. The BUCCAL BR(S). OF VII passes superficial to the masseter m. IT SHOULD NOT BE CONFUSED WITH THE BUCCAL N. (A BR. OF V3) which is purely sensory and enters the cheek deep to the masseter.
Main trunk of VII
TO ZANZIBAR BY MOTOR CAR
Buccal branches
Marginal mandibular branch
Cervical branch

25. VESSELS

26. MAXILLARY ARTERY MAXILLARY A. BRANCHES OF 1ST (MANDIBULAR) PART
Lateral pterygoid a. and m.
Ant. and post. deep temporal aa.
Masseteric a.
Middle meningeal a.
Maxillary a.
Infraorbital a.
Post. superior alveolar a.
Inferior alveolar a.
Buccal a.
Medial pterygoid a. and m.
The CHIEF ARTERY OF THE INFRATEMPORAL FOSSA IS THE MAXILLARY A., one of the terminal brs. of the ext. carotid a. THE MAXILLARY A. HAS THREE PARTS: 1) MANDIBULAR PART (passes deep to neck of mandible) 2) PTERYGOID PART (usually, as depicted here, passes superficial to the lat. pterygoid m.) and 3) PTERYGOPALATINE PART (passes into the pterygopalatine fossa). Only the first two parts lie in the infratemporal fossa and will be considered here.
The MANDIBULAR PART of the maxillary a. has several brs., the most imp. of which are the inf. alveolar a. (which supplies the mandibular teeth) and the mid. meningeal a. (which supplies the dura mater).
The PTERYGOID PART of the maxillary a. has muscular brs. These are the ant. and post. deep temporal aa., masseteric a., med. and lat. pterygoid aa., and the buccal a. Many of these small arteries are difficult to find in the lab.
Ext. carotid a.
MAXILLARY A.
BRANCHES OF 1ST (MANDIBULAR) PART
BRANCHES OF 2ND (PTERYGOID) PART
BRANCHES OF 3RD (PTERYGOPALATINE) PART

27. RELATIONSHIPS OF MIDDLE MENINGEAL A.
Auriculotemporal n.
Maxillary a.
In this deep dissection note the COURSE AND RELATIONSHIPS OF THE MID. MENINGEAL A. It passes superiorly between the two roots of the auriculotemporal n. on its way to the f. spinosum. This artery/nerve relationship is quite constant and is a good way to identify these structures in the lab.
Ext. carotid a.

28. MIDDLE MENIGEAL A. SUPPLIES DURA MATER
1. Most of the dura mater is supplied by the MID. MENINGEAL A. This artery also supplies the bones of the calvaria.
Ant. & post. branches
of middle meningeal a.

29. PTERION: LANDMARK FOR MIDDLE MENINGEAL A.
The middle meningeal a. is clinically imp. b/c it is often torn in skull fractures (especially fractures in the region of the pterion, which overlies the anterior branch of the middle meningeal a. and where the bone is quite thin). The pterion is located two fingerbreadths above the zygomatic arch and a thumb breadth behind the frontal process of the zygomatic bone.

30. EPIDURAL (EXTRADURAL) HEMORRHAGE
HEMORRHAGE within the cranial cavity is extremely serious because the soft brain may become compressed by accumulating blood. EPIDURAL HEMORRHAGE is due to laceration of the mid. meningeal a. Because of the high arterial pressure blood collects rapidly in the epidural space and death will result if the condition is not treated immediately.

31. PTERYGOID PLEXUS OF VEINS
Post. sup. alveolar v.
Superficial temporal v.
Pterygoid plexus
Maxillary vv.
Retromandibular v.
Inf. alveolar v.
The PTERYGOID PLEXUS is a network of veins in the infratemporal fossa. It receives numerous tributaries corresponding to the branches of the maxillary a. These include the inf. alveolar v. draining the mandibular teeth and the superior alveolar vv. draining the maxillary teeth. Dental infections can therefore spread to the pterygoid plexus. The plexus is drained posteriorly by the maxillary v.(vv.). The maxillary v. joins the superficial temporal v. to form the retromandibular v. (within the parotid gl.).

32. COMMUNICATIONS OF PTERYGOID PLEXUS
Cavernous
sinus
Inf. ophthalmic v.
Emissary vv.
(via f. ovale)
The pterygoid plexus has communications with other veins in the head and neck. These include a communication with the facial v. via the deep facial v. (vv.), with the inf. ophthalmic v. in the orbit (via a connection that passes through the inf. orbital fissure), and with the cavernous sinus in the cranial cavity (via an emissary v. that passes through the f. ovale). Infections from the face and orbit can spread to the pterygoid plexus via these pathways, and then pass into the cranial cavity.
Facial v.
Pterygoid
plexus
Deep facial vv.

33. CAVERNOUS SINUS (CORONAL SECTION)
III IV
Int. carotid a.
This is a CORONAL SECTION THROUGH THE CAVERNOUS SINUS SHOWING ITS IMPORTANT RELATIONSHIPS. Commit it to your memory ! Note that the two sinuses lie on either side of the body of the sphenoid (which contains the sphenoidal air sinus). PASSING THROUGH THE SINUS ARE THE INT. CAROTID A. AND VI. EMBEDDED WITHIN THE DURA MATER FORMING THE LATERAL WALL OF THE SINUS ARE III, IV, OPHTHALMIC N. (V1) AND MAXILLARY N (V2). Infections in the cavernous sinus can affect any of the structures closely related to it. Prior to the advent of antibiotics infectious cavernous sinus thrombosis was nearly always fatal.
V2 (Maxillary n.)
V1 (Ophthalmic n.)
Sphenoid sinus
VI (abducens)
Hypophysis

34. TEMPOROMANDIBULAR
JOINT

35. ARTICULATING BONES OF TMJ
SQUAMOUS TEMPORAL BONE
Articular tubercle
Mandibular fossa
(articular part)
Postglenoid tubercle
The TMJ is a modified hinge type of synovial joint between the HEAD OF THE MANDIBLE and the SQUAMOUS PART OF THE TEMPORAL BONE. The parts of the squamous temporal involved in the joint are the mandibular fossa (articular part), articular tubercle (a ridge of bone anterior to the mandibular fossa) and the postglenoid tubercle (a bony projection posterior to the mandibular fossa).
The mandibular fossa also has a nonarticular part. The nonarticular part is formed by the tympanic portion of the temporal bone (the curved plate of bone forming the floor and ant. wall of the ext. acoustic meatus). It contains the glenoid pr. of the parotid gland.
TYMPANIC TEMPORAL BONE
(nonarticular part
of mandibular fossa)
HEAD OF MANDIBLE

36. LIGAMENTS, NERVES & BLOOD SUPPLY OF TMJ
Joint capsule
Lateral (temporomandibular) lig.
Sphenomandibular lig.
Styloid process
Stylomandibular lig.
V3 and otic ganglion
Joint
capsule
Mid. meningeal a.
Auriculotemporal n.
Maxillary a.
Inferior alveolar n.
The TMJ has a fibrous capsule which is thin and loose except laterally where it is thickened to form the LATERAL (TEMPOROMANDIBULAR) LIG. This INTRINSIC LIG. is fan-shaped, with the base attached to the zygomatic pr. of the temporal bone and the apex to the neck of the mandible. Some of the fibers of the lateral lig. run posteroinferiorly; they serve to restrict retraction of the mandible and therefore protect the structures directly behind the TMJ (eg, parotid gl.) from compression.
The TMJ has TWO EXTRINSIC LIGS. The STYLOMANDIBULAR LIG. is a thickening of the deep cervical fascia (specifically, the deep part of the parotid fascia) and runs from the styloid pr. to the angle of the mandible. It separates the parotid and submandibular gls. The SPHENOMANDIBULAR LIG. passes from the spine of the sphenoid to the lingula. This lig. is a remnant of the cartilage of pharyngeal arch 1. The sphenomandibular lig. and lingula act as a funnel to direct anesthetic solution into the mandibular f. when administering an inf. alveolar n. block. The two extrinsic ligs. do not provide much support for the TMJ.
The NERVE SUPPLY TO THE TMJ is the auriculotemporal n. and the masseteric n. (not shown). The BLOOD SUPPLY is from the maxillary and superficial temporal aa. (not shown).
Lingual n.
Sphenomandibular lig.
Stylomandibular lig.
INTRINSIC LIGAMENT
Mylohyoid a. and n.
EXTRINSIC LIGAMENTS

37. MOVEMENTS OCCURRING AT TMJ
Lower joint compartment (hinge action)
Upper joint compartment (gliding action)
Articular disc
Articular tubercle
Articular tubercle
Joint capsule A.
JAWS CLOSED
Fig. A.
The CAVITY OF THE TMJ IS DIVIDED INTO TWO COMPARTMENTS (SUP. & INF.) BY THE PRESENCE OF AN ARTICULAR DISC. The disc is composed of avascular fibrous tissue; the articular surfaces of the temporal bone and head of the mandible are also covered with this type of tissue. Avascular fibrous tissue is adapted to resist the compressive forces this joint is subjected to, and makes the TMJ unusual compared to other synovial joints where the bones are covered with hyaline cartilage. The fibrous (joint) capsule is lined by synovial membrane in both joint compartments.
Fig. B.
A HINGE ACTION occurs in the INF. COMPARTMENT. The head of the mandible rotates (like a hinge) on the inf. surface of the articular disc. This occurs when the jaw is slightly opened.
Fig. C.
 A GLIDING ACTION occurs in the SUP. COMPARTMENT. The head of the mandible and the articular disc glide forward onto the inf. surface of the articular tubercle. This is due to the pull of the lat. pterygoid m. and occurs (along with the hinge action) when the jaw is widely opened. C.
JAWS WIDELY OPENED
(HINGE AND GLIDING ACTION COMBINED) B.
JAWS SLIGHTLY OPENED
(HINGE ACTION PREDOMINATES)

38. MOVEMENTS OCCURRING AT TMJ
Note that when the lower jaw is opened widely the head of the mandible and the articular disc glide forward beneath the articular tubercle.

39. DISLOCATION OF TMJ
DISLOCATION OF THE TMJ sometimes occurs when the head of the mandible and articular disc are beneath the articular tubercle. If they should "slip off" anteriorly from the tubercle (as may occur during a wide yawn) they come to lie in the infratemporal fossa . The TMJ is the only joint which can be dislocated without an external force. Dislocation of the TMJ is almost always bilateral and anterior (GGO, 4th ed., p. 667). The lateral (temporomandibular) lig. and the postglenoid tubercle help prevent posterior dislocation. The spine of the sphenoid helps prevent medial displacement. Once dislocated, the TMJ is notorious for repeat dislocations.

40. RELATIONSHIPS OF TMJ (CORONAL SECTION)
Middle cranial fossa
(superior)
Mandibular fossa
Articular disc
Skin
(lateral)
Spine of sphenoid
(medial)
Note the following relationships of the TMJ: (GGO)
Superior: Thin bone of mandibular fossa (articular part) separates the head of the mandible and articular disc from the middle cranial fossa. Hence a blow to the mandible from below could drive the head of the mandible into the cranial cavity.
Anterior: Lateral pterygoid m. inserts into the articular disc and pterygoid fovea of the mandible.
Medial: Spine of sphenoid.
Lateral: Skin.
Posterior (not shown): Parotid gland (glenoid process), auriculotemporal n., superficial temporal vessels.
Lateral pterygoid m.
(anterior)
Maxillary a. & v.

41. END OF LECTURE