TEMPORAL AND INFRATEMPORAL FOSSAE (Grant's Dissector [16th Ed.] pp. 256-262) TODAY’S GOALS: 1. Identify the boundaries and bony landmarks of the temporal and infratemporal fossae 2. Identify the muscles of mastication 3. Identify the maxillary artery and its major branches, along with the pterygoid venous plexus and maxillary vein 4. Identify the branches of the mandibular division of the trigeminal nerve [CN V3] 5. Identify the temporomandibular joint, its articular disc, and compartments DISSECTION NOTES: General comments: Perform today’s dissection on the side of the head that the parotid gland had been previously removed (from the last lab session). Access to the temporal and infratemporal fossae will be accomplished by making saw cuts: (a) through the zygomatic bone and arch and reflecting the masseter muscle inferiorly, and (b) through the coronoid process, (c) neck, and (d) upper half of ramus of the mandible (see Dissector pp. 258, 259, Figs. 7.30 and 7.31). In preparation for this work, review the following osteology and landmarks. I. Osteology A. Temporal fossa 1. Bony landmarks and boundaries • Temporal fossa (shallow depression on lateral aspect of skull formed by portions of the parietal, frontal, squamous portion of the temporal, and greater wing of sphenoid bones) • Superior temporal line – upper attachment of temporal fascia • Inferior temporal line – upper attachment of temporalis muscle • Zygomatic arch – bony arch formed by fusion of the zygomatic process of the temporal bone and the temporal process of the zygomatic bone A horizontal plane between the zygomatic arch and lateral surface of the skull forms the boundary between the temporal fossa and infratemporal fossa. B. Mandible (Dissector p. 257, Fig. 7.28) 1. Bony landmarks • Ramus – coronoid process, head (condyle), neck, mandibular notch, mandibular foramen • Body – alveolar process, mandibular canal, mental foramen, mylohyoid groove • Angle – junction between the horizontal body and vertical ramus of mandible C. Infratemporal fossa (Dissector p. 257, Fig. 7.29) 1. Bony landmarKs and boundaries • Anteriorly – posterior surface of maxilla • Posteriorly – external acoustic meatus and styloid process • Medially – lateral plate of the pterygoid process of the sphenoid bone • Superiorly – undersurface (infratemporal surface) of the greater wing of sphenoid • Laterally – ramus of mandible 16 2. Foramina/Openings • Mandibular foramen – for the inferior alveolar n,a,v • Pterygomaxillary fissure – for transmission of maxillary artery into the pterygopalatine fossa • Inferior orbital fissure – for passage of the infraorbital artery to the floor of the orbit • Foramen ovale – for passage of the mandibular nerve (CN V3) and the lesser petrosal nerve (branch of CN IX) • Foramen spinosum – for the middle meningeal artery (MMA) II. Dissection Steps to Revealing the Contents of the Temporal and Infratemporal Fossae A. Masseteric region – For saw cuts, refer to Dissector p. 258, Fig. 7.30: First, incise the tough connective tissue along the superior border of the zygomatic arch and insert a probe or tine of a forcep behind the arch. Slide it against the inner surface of the arch as far anteriorly and posteriorly as possible. At each end, cut down to the probe with an electric bone saw. Reflect the arch and attached masseter muscle inferiorly to its insertion on the lateral surface and angle of the ramus of the mandible. Observe that the masseteric nerve and vessels enter the deep surface of the masseter as they pass over the mandibular notch. These will be torn during this reflection. B. Temporal Fossa With reflection of the masseter muscle, you can now view the fan-shaped temporalis muscle and its insertion into the coronoid process. Using a bone saw, cut this process and lift the temporalis superiorly (Dissector p. 259, Fig. 7.31). Observe the deep temporal vessels and nerves entering its deep surface between the muscle and skull bone. Cut the neck of the mandible and the ramus (above the mandibular foramen) for viewing of contents of the infratemporal fossa. (Dissector p. 259, Fig. 7.31) • Temporalis muscle – fills the temporal fossa (origin) and descends medial to the zygomatic arch and inserts into the coronoid process and anterior border of the ramus of the mandible • Deep temporal vessels and nerves (anterior and posterior) – branches of the maxillary artery and mandibular nerve (V3) and pass upwards on the deep surface of the temporalis between it and the skull bone (Dissector pp. 260, 261 Figs. 7.32, 7.33). C. Infratemporal fossa Before proceeding to disturb the field, observe whether the maxillary artery is visible superficial to the lateral pterygoid muscle (occurs in about 2/3s of individuals). If not immediately visible, it can be found coursing deep to the lateral pterygoid muscle (occurs in about 1/3 of individuals) [In this case, the muscle must be removed in a piecemeal fashion in order to protect and visualize the artery].Next, look for a “network” of small anastomotic veins overlying the lateral pterygoid muscle. These represent the pterygoid venous plexus. This plexus consolidates into a short maxillary vein or two that courses behind the neck of the mandible in company with the maxillary artery. It will join the superficial temporal vein to form the retromandibular vein. 17 Now proceed to find the following contents (Dissector pp. 260, 261; Figs. 7.32, 7.33): • Lateral pterygoid muscle – its fibers are “horizontal” in orientation. Note that it has two heads: Superior head attaches to the undersurface of the greater wing of sphenoid and inserts into the articular capsule and disc of the temporomandibular joint (TMJ). Shave off the lateral aspect of the TMJ capsule and identify the articular disc and superior and inferior compartments of this joint cavity. Inferior head attaches from the lateral surface of the lateral pterygoid plate and inserts into the necK/fovea of the mandible. (Dissector p. 262, Fig. 7.34) • Medial pterygoid muscle – its fibers are “oblique” in orientation. They arise from the medial surface of the lateral pterygoid plate and insert into the medial surface of the ramus and angle of the mandible inferior to the mandibular foramen. • CN V3 and its branches. The mandibular nerve enters the infratemporal fossa via the foramen ovale and will therefore be obscured from view unless the lateral pterygoid muscle is removed. Before disturbing this muscle look for the following branches of V3 and their relationships: o Deep temporal nerves (anterior and posterior) – these typically pass upward between the superior head of the lateral pterygoid muscle and the skull bone to the deep surface of the temporalis muscle o Muscular branches to mm of mastication – small branches of the mandibular nerve supply the medial and lateral pterygoid muscles (don’t look for these) o Buccal nerve (aka Long buccal nerve) – a sensory nerve that emerges between the superior and inferior heads of the lateral pterygoid and courses downward on the external surface of buccinator. Its branches penetrate this muscle to supply sensory innervation to the mucosal surface of the cheek and other fibers project to the skin of the cheek. This nerve often courses with the buccal artery (a branch of the maxillary artery). o Inferior alveolar nerve – it can be found emerging along the lower border of the lateral pterygoid muscle between it and the medial pterygoid. Follow its course to the mandibular foramen. Just prior to entering this foramen look for its mylohyoid branch (a motor nerve) to the mylohyoid and anterior digastric muscles. o Lingual nerve – can also be found emerging along the lower border of the lateral pterygoid muscle between it and the medial pterygoid. It courses anterior and medial to the inferior alveolar nerve. We will follow its course into the oral cavity later. o Auriculotemporal nerve – emerges from behind the lateral pterygoid and courses behind the neck of the mandible into the upper portion of the parotid gland. After providing parotid branches (conveying secretomotor fibers from the otic ganglion) to the gland, it ascends over the root of the zygomatic arch posterior to the superficial temporal vessels. In its course it also gives rise to sensory fibers to the TMJ capsule, external ear, and skin of the temporal region. It often forms from a pair of “roots” that enclose the middle meningeal artery. 18 • Maxillary artery – despite its many branches (several of which are muscular to the muscles of mastication) attempt to find its major branches: o Inferior alveolar – can be seen to course with the inferior alveolar nerve to the mandibular foramen o Middle meningeal artery – arises from the superior border of the maxillary artery usually opposite the origin of the inferior alveolar branch. It courses posteriorly and superiorly behind the lateral pterygoid enroute to the foramen spinosum. It is the principal blood supply to the cranial dura and will be seen in the next lab period. o Buccal artery – courses toward the cheek in company with the buccal branch of CN V3. o Deep temporal branches (anterior and posterior) – course with corresponding nerves to the temporalis o Posterior superior alveolar branches – can be observed coursing along the posterior surface of the maxilla and entering the posterior superior alveolar foramina Follow the course of the maxillary artery medially where it enters the pterygopalatine fossa via the pterygomaxillary fissure. The remaining branches of the maxillary artery will be described later. • Otic ganglion – a parasympathetic ganglion located on the deep (medial) surface of the mandibular nerve (don’t look for it). It contains cell bodies of postganglionic parasympathetic neurons. Following their synapse with preganglionic fibers contained within the lesser petrosal nerve, postganglionic axons will “hitchhike” along the auriculotemporal nerve and leave this nerve via parotid branches into the parotid gland. • Chorda tympani – a branch of the facial nerve which exits the petrotympanic fissure and unites with lingual nerve.