#14 - Infratemporal Fossa

  1. Review the terminal branches of the facial nerve, the parotid gland and its duct. Cut the duct and reflect it anteriorly. Cut the nerves and reflect them posteriorly. Observe the masseter muscle (926/N50) and note its attachment to the zygomatic arch (N50). Make cuts (N50) with an autopsy saw through the zygomatic arch just anterior and posterior to the origin of the masseter muscle (observe the arch on a skeleton so cuts can be slanted properly). Pushing a probe medial to the arch to ascertain that the position of the anterior cut will avoid entrance into the orbit. See diagram.
  2. Carefully reflect the severed zygomatic arch and the attached masseter muscle laterally and inferiorly in order that the masseteric artery and nerve (N50) can be seen entering the deep surface of the muscle by way of the mandibular notch (N50). The artery and nerve must be cut in order to continue the reflection; peel the periosteum and muscle from the ramus of the mandible.
  3. Removal of the zygomatic arch reveals the insertion of the temporalis muscle (926/N50) into the coronoid process of the mandible (N50). Locate the buccal nerve (922/N42), branch of the mandibular division of V (N42) that often is found fused to the fascia around the insertion of the temporalis muscle, or may even pass through the substance of the muscle. The nerve should be dissected away from the muscle and followed into the buccinator muscle (852/N42). It is not the motor supply to the buccinator, but sensory to the cheek.
  4. Make a cut through the tip of the coronoid process (N50, cut #1) and that portion of the temporalis muscle deep to it. Reflect this piece of bone and the temporalis muscle superiorly. The temporalis muscle is considerably thicker than it appears from the surface and it attaches not just to the coronoid process but also well down on the ramus. Deep temporal nerves supplying the muscle lie against the periosteum of the skull.
  5. With a saw make a cut through the neck of the condyloid process of the mandible (N50, cut #2). The third cut is across the ramus of the mandible above the orifice of the mandibular foramen (N50, cuts #3 & 4). Because this orifice is on the medial side of the ramus and cannot be visualized, the safer approach is to make two cuts, the first a little high to identify the inferior alveolar nerve and artery (923 & 920/N41) and dissect it away from the bone and then make the 2nd cut lower, but still above the mandibular foramen. These three cuts allow you to remove a piece of the ramus of the mandible to give access to the infratemporal fossa. Care should be taken in sawing the ramus to make this opening as large as possible but avoiding cutting the inferior alveolar nerve and artery entering the mandibular foramen. Preservation of the inferior alveolar nerve is desirable. To facilitate exposure both mandibular rami must be sawed.
  6. Remove the buccal fat pad and the pterygoid plexus of veins, with blunt dissection, to expose the contents of the infratemporal fossa. Locate the maxillary artery (920/N36), coursing between the sphenomandibular ligament (923/N14 - the ligament is an embryonic remnant of the first branchial arch skeleton which did not ossify) and the mandible, and crossing the superficial surface of the lateral pterygoid muscle (920/N36). It is usually embedded in tough fascia. About half of infratemporal fossae will feature the artery deep to the lateral pterygoid muscle, and, if so, its dissection must be delayed until after the latter muscle has been removed. When the maxillary artery courses deep to the lateral pterygoid a Y-shaped artery is evident on the surface of the lateral pterygoid which branches into the inferior alveolar and temporal arteries.
    There are small branches of the artery to the muscles of mastication, the middle ear and the lower teeth. Removal of the fascia from the main trunk usually removes many of these branches.
  7. Cut the maxillary artery (if it courses superficial to the lateral pterygoid muscle) and reflect it superiorly and inferiorly, fully exposing the lateral pterygoid muscle. Note the two heads of the lateral pterygoid (N36) and its attachment not only to the condyloid process but also to the articular disc (923/N14) in the temporomandibular joint (N14). Remove both heads of the lateral pterygoid muscle by picking them away with a hemostat, but preserve the buccal nerve (N42) which passes between the heads. If the maxillary artery courses deep to this muscle, it will be exposed at this time. In either case the important middle meningeal artery (920/N36) can now be followed to the foramen spinosum (N8). There may be an accessory meningeal artery as well that traverses the foramen ovale.
  8. Following the prominent inferior alveolar and lingual nerves (923/N42) upward to the foramen ovale (N8) will lead to anterior and posterior divisions of the mandibular division of the trigeminal nerve (N42), separated by a ligament, and the undivided trunk.
  9. Locate as many of the following branches of the mandibular division as you can:
    1. Undivided trunk.
      1. Medial pterygoid - difficult to locate.
    2. Anterior division.
      1. Buccal (N42) - emerged between removed heads of lateral pterygoid.
      2. Anterior deep temporal (N42) - against periosteum of greater wing of sphenoid.
      3. Posterior deep temporal (N42) - against periosteum of greater wing of sphenoid.
    3. Posterior division.
      1. Auriculotemporal (N42) - usually splits around middle meningeal artery.
      2. Lingual (N42).
  10. Branches to the tensor tympani muscle and the tensor of the palate are not ordinarily found. Special approach is required to display the otic ganglion (N42) which lies on the medial side of the undivided trunk close to the foramen ovale. It is too difficult to display for this course, but its function should be understood.
  11. Follow the maxillary artery (N42) until it terminates as it disappears into the pterygopalatine fossa (N4) through the pterygomaxillary fissure (950/N4). Just before doing so, it gives an posterior superior alveolar branch (N36) to posterior upper teeth. The posterior superior alveolar nerve (N41) and artery (922/N36) enter small foramina on the infratemporal surface of the maxilla to reach the molar teeth. The nerve from the maxillary division of the trigeminal has emerged from the pterygomaxillary fissure.
  12. Locate the chorda tympani nerve (923/N42) joining the back side of the lingual nerve after emerging from the middle ear (N42) through the petrotympanic fissure (N8).
  13. Locate the mylohyoid nerve (N42), branching from the inferior alveolar nerve. Just before the inferior alveolar nerve enters the mandibular foramen it gives off the mylohyoid nerve that courses toward the mylohyoid muscle by passing medial to the body of the mandible.
  14. The medial pterygoid muscle (920/N51) can now be observed.
  15. With a needle, imitate the dentist injecting anesthetic near the inferior alveolar nerve. Ascertain what structures are pierced.