Short, thick, conical muscle; apex pointing backwards. Key muscle of infratemporal region — its relations define the layout of all major structures in the infratemporal fossa. Only masticatory muscle that opens the mouth.

Origin (Two Heads)

Gap between heads: maxillary artery + buccal nerve pass through

Insertion

• Pterygoid fovea — depression on anterior neck of mandible
• Articular disc + capsule of TMJ

Articular disc = developmentally degenerated part of lateral pterygoid tendon; lower head passes between the two heads of medial pterygoid

Nerve Supply

• Branch of anterior division of mandibular nerve (CN V3)

Actions

Relations — Key Muscle of Infratemporal Fossa

Superficial (lateral): ramus of mandible, masseter, tendon of temporalis, superficial head of medial pterygoid, maxillary artery (+ temporal/masseteric branches)

Deep (medial): mandibular nerve, middle meningeal artery, sphenomandibular ligament, deep head of medial pterygoid

Upper border: deep temporal nerves (×2) + arteries; masseteric nerve + artery

Lower border: inferior alveolar nerve + artery; lingual nerve; middle meningeal artery (passes upward deep to lower border)

Gap between heads:

Maxillary artery divided into 3 parts by lower head: 1st (mandibular) = below; 2nd (pterygoid) = on/deep to lower head; 3rd (pterygopalatine) = above, through gap

Pterygoid venous plexus — surrounds lateral pterygoid; communicates with cavernous sinus (via emissary veins through foramina ovale + spinosum), facial vein (via deep facial vein), inferior ophthalmic vein (via inferior orbital fissure)

Relation to TMJ

• Dual insertion: pterygoid fovea + articular disc/capsule
• Dislocation: excessive contraction of both lateral pterygoids → condyle slips anterior to articular tubercle
• Unilateral contraction: disc + condyle pulled anteromedially → contralateral chin deviation

Applied Anatomy

• Trismus — infection/trauma/tumour in infratemporal fossa involving lateral pterygoid; or post-injection fibrosis after inadvertent injection (dental inferior alveolar nerve blocks)
• TMJ dislocation — both condyles pulled forwards beyond articular tubercle; reduced by pressing thumbs down on lower molars while pushing chin upward (Hippocratic method)
• Pterygoid venous plexus — dental/tonsillar infection → cavernous sinus via plexus → cavernous sinus thrombosis; haematoma from plexus injury during inferior alveolar nerve blocks → trismus

The lateral pterygoid is a short, thick, conical muscle with its apex pointing backwards. It is the key muscle of the infratemporal region — its relations define the layout of all major structures in the infratemporal fossa. It is the only muscle of mastication that opens the mouth (depresses the mandible).

Location

Lies within the infratemporal fossa, passing backwards and slightly laterally from the roof and medial wall of the fossa to the neck of the mandible.

Origin — Two Heads

The two heads are separated by a gap through which the maxillary artery and buccal nerve pass.

Insertion

The fibres of both heads run backwards and laterally, converging to a thick tendon that inserts into:

1. Pterygoid fovea — depression on the anterior aspect of the neck of the mandible
2. Articular disc and capsule of the temporomandibular joint

The articular disc of the TMJ is developmentally a degenerated part of the tendon of the lateral pterygoid. The lower head of the lateral pterygoid passes between the two heads of the medial pterygoid.

Nerve Supply

Branch of the anterior division of the mandibular nerve (CN V3).

Actions

Relations — The Key Muscle of the Infratemporal Fossa

The lateral pterygoid’s relations describe the entire infratemporal fossa.

Superficial (Lateral) Relations

Deep (Medial) Relations

Structures Emerging at the Upper Border

Structures Emerging at the Lower Border

Structures Passing Through the Gap Between the Two Heads

The maxillary artery is divided into 3 parts by the lower head of the lateral pterygoid: 1st part (mandibular) — below; 2nd part (pterygoid) — on or deep to the lower head; 3rd part (pterygopalatine) — above, passing through the gap.

Pterygoid Plexus of Veins

The pterygoid venous plexus surrounds the lateral pterygoid muscle. It receives tributaries corresponding to all branches of the maxillary artery and communicates with:

• The cavernous sinus (via emissary veins through foramina ovale and spinosum)
• The facial vein (via the deep facial vein)
• The inferior ophthalmic vein (via inferior orbital fissure)

Relation to the TMJ

The lateral pterygoid has a unique dual insertion — into both the pterygoid fovea of the mandibular neck and the articular disc/capsule of the TMJ. This is why:

• Dislocation of the TMJ (condyle slips anterior to the articular tubercle) is caused by excessive contraction of both lateral pterygoids.
• In unilateral contraction, the disc and condyle are pulled anteromedially, producing contralateral deviation of the chin.

Applied Anatomy

Trismus (inability to open the mouth) may result from:

• Infection, trauma, or tumour in the infratemporal fossa involving the lateral pterygoid.
• Post-injection fibrosis following inadvertent injection into the muscle (dental inferior alveolar nerve blocks).

TMJ dislocation:

• Both lateral pterygoids pull condyles forwards beyond the articular tubercle, locking them open — patient unable to close the mouth.
• Reduced by pressing the thumbs down on lower molar teeth while pushing the chin upward (Hippocratic method).

Pterygoid venous plexus — clinical relevance:

• Spread of dental or tonsillar infection can reach the cavernous sinus via this plexus → cavernous sinus thrombosis.
• Haematoma from pterygoid plexus injury during inferior alveolar nerve blocks can cause trismus.

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