Medial Pterygoid
Thick, quadrilateral masticatory muscle. Medial counterpart of masseter — together they form a pterygomasseter sling around the angle of the mandible → powerful elevation (mouth closure).
Origin (Two Heads)
| Head | Origin |
|---|---|
| Deep (large, bulk) | Medial surface of lateral pterygoid plate + grooved surface of pyramidal process of palatine bone |
| Superficial (small slip) | Maxillary tuberosity + lateral surface of pyramidal process of palatine bone |
Two heads enclose lower head of lateral pterygoid between them
Insertion
- Fibres run downwards, backwards, laterally → roughened area on posteroinferior medial surface + angle of ramus of mandible (up to mandibular foramen, forwards to mylohyoid groove)
Nerve Supply
- Nerve to medial pterygoid — from main trunk of mandibular nerve (CN V3) before it divides; also supplies tensor veli palatini + tensor tympani (via otic ganglion, without relay)
Actions
| Action | Mechanism |
|---|---|
| Elevates mandible (closes mouth) | Both medial pterygoids |
| Protrudes mandible | Both medial + lateral pterygoids |
| Side-to-side grinding | Medial + lateral pterygoids of opposite sides alternately |
| Lateral excursion | Medial + lateral pterygoids of one side → mandible rotates forward + to opposite side |
Relations
Superficial (lateral): lingual nerve, inferior alveolar nerve, inferior alveolar vessels; lower down, separated from ramus by lingual nerve, inferior alveolar nerve, maxillary artery, sphenomandibular ligament
Deep (medial): tensor veli palatini, levator veli palatini, superior constrictor of pharynx, styloglossus, stylopharyngeus
Comparison with Masseter
| Feature | Masseter | Medial Pterygoid |
|---|---|---|
| Location | Lateral to ramus | Medial to ramus |
| Origin | Zygomatic arch | Pterygoid fossa (medial lat. pterygoid plate + maxillary tuberosity) |
| Insertion | Lateral ramus surface | Medial ramus surface |
| Nerve | Masseteric nerve (anterior division V3) | Nerve to medial pterygoid (main trunk V3) |
| Primary action | Elevates mandible | Elevates mandible |
| Together | Form pterygomasseter sling around angle of mandible |
Applied Anatomy
- Trismus — inflammation/haematoma involving medial pterygoid (post inferior alveolar nerve block, peritonsillar abscess, parapharyngeal space infection) → painful spasm
- Pterygomandibular space — between medial pterygoid (medial) and ramus of mandible (lateral); inferior alveolar nerve + lingual nerve descend through it; target for inferior alveolar nerve block (dental injection); infection → trismus + dysphagia
- Peritonsillar abscess (Quinsy) — spreads to superior constrictor + medial pterygoid → severe trismus = hallmark sign
The medial pterygoid is a thick, quadrilateral muscle of mastication lying in the infratemporal fossa. It is the medial counterpart of the masseter — together they form a muscular sling around the angle of the mandible, suspending it between them and producing powerful elevation (mouth closure).
Origin — Two Heads
| Head | Origin |
|---|---|
| Deep head (large, forming the bulk) | Medial surface of the lateral pterygoid plate and grooved surface of the pyramidal process of the palatine bone |
| Superficial head (small slip) | Maxillary tuberosity and lateral surface of the pyramidal process of the palatine bone |
The two heads enclose the lower head of the lateral pterygoid between them — the lower head of lateral pterygoid passes between the superficial and deep heads of the medial pterygoid.
Insertion
The fibres run downwards, backwards, and laterally, converging on a strong tendinous lamina that inserts into the roughened area on the posteroinferior part of the medial surface and angle of the ramus of the mandible — as high as the mandibular foramen and as far forwards as the mylohyoid groove.
Nerve Supply
Nerve to medial pterygoid — a branch from the main trunk of the mandibular nerve (CN V3), given off before the nerve divides into anterior and posterior divisions. This branch also supplies tensor veli palatini and tensor tympani (passing through the otic ganglion without relay).
Actions
| Action | Mechanism |
|---|---|
| Elevates mandible (closes mouth) | Both medial pterygoids acting together |
| Protrudes mandible | Both medial + lateral pterygoids acting together |
| Side-to-side (grinding) movements | Medial and lateral pterygoids of opposite sides contracting alternately |
| Lateral excursion | Medial + lateral pterygoids of one side → mandible rotates forwards and to the opposite side |
Together with the masseter, the medial pterygoid forms a pterygomasseter sling around the angle of the mandible, generating the powerful biting force needed for mastication.
Relations
Superficial (Lateral) Relations
| Structure |
|---|
| Lingual nerve |
| Inferior alveolar nerve |
| Inferior alveolar vessels |
| Ramus of mandible (lower down, separated by lingual and inferior alveolar nerves, maxillary artery, and sphenomandibular ligament) |
In the upper part, the medial pterygoid is separated from the lateral pterygoid by the lateral pterygoid plate and by the lingual and inferior alveolar nerves. Lower down, it is separated from the ramus of the mandible by the lingual nerve, inferior alveolar nerve, maxillary artery, and sphenomandibular ligament.
Deep (Medial) Relations
| Structure |
|---|
| Tensor veli palatini |
| Levator veli palatini |
| Superior constrictor of pharynx |
| Styloglossus |
| Stylopharyngeus |
Comparison with Masseter
| Feature | Masseter | Medial Pterygoid |
|---|---|---|
| Location | Lateral to ramus | Medial to ramus |
| Origin | Zygomatic arch | Pterygoid fossa (medial surface of lateral pterygoid plate + maxillary tuberosity) |
| Insertion | Lateral surface of ramus | Medial surface of ramus |
| Nerve supply | Masseteric nerve (anterior division CN V3) | Nerve to medial pterygoid (main trunk CN V3) |
| Primary action | Elevates mandible | Elevates mandible |
| Together | Form the pterygomasseter sling around the angle of the mandible |
Applied Anatomy
Trismus:
- Inflammation or haematoma involving the medial pterygoid (e.g., post inferior alveolar nerve block, peritonsillar abscess, or parapharyngeal space infection) causes painful spasm and inability to open the mouth.
- The medial pterygoid lies close to the pterygomandibular space — a common site for spread of dental infection.
Pterygomandibular Space:
- The space between the medial pterygoid (medially) and the ramus of the mandible (laterally) is the pterygomandibular space.
- The inferior alveolar nerve and lingual nerve descend through this space before entering their respective foramina.
- This is the target space for the inferior alveolar nerve block (dental injection).
- Infection in this space → trismus, dysphagia, medial pterygoid spasm.
Peritonsillar abscess (Quinsy):
- Spreads medially from the tonsillar fossa and can involve the superior constrictor and medial pterygoid, causing severe trismus — a hallmark clinical sign.
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