(4.27)

Now we'll move on to look at the third division of the trigeminal, the mandibular nerve. Here's the mandibular nerve leaving the trigeminal ganglion. The mandibular nerve passes downward through the foramen ovale. The foramen ovale emerges under here. The foramen is just behind the root of the lateral pterygoid plate.

Returning to the dissection, here's the mandibular nerve, branching as it emerges from the foramen ovale. The mandibular nerve has both motor and sensory branches. Its motor branches (here they are) go to the muscles of mastication: masseter, temporalis, and the pterygoid muscles. Small branches, not seen here, supply tensor tympani and tensor palati.

The other branches of the mandibular nerve are almost entirely sensory. This branch is the buccal nerve. It runs downward and forwards to supply sensation to the cheek, both outside and inside.

This branch is the auriculo-temporal nerve. It passes deep to the neck of the mandible, which is here, then runs upwards to supply sensation to this region on the side of the head.

This leaves two major branches which run downward on the medial pterygoid muscle. They're the inferior alveolar nerve, and just in front of it, the lingual nerve.

Seen from the inside, the lingual nerve is here, the inferior alveolar nerve is here. The insertion of the medial pterygoid muscle is here. The inferior alveolar nerve follows the medial pterygoid muscle down toward the mandible.

It enters the mandible through this opening, the mandibular foramen. As it enters the bone, the inferior alveolar nerve lies just behind this projection, the lingula. To follow the course of the inferior alveolar nerve in the mandible, we'll remove the overlying bone.

Here's the inferior alveolar nerve entering its tunnel in the bone, the mandibular canal. Just before it does so it gives off this mylohyoid branch, which runs downwards in this groove to supply the mylohyoid muscle and the anterior belly of the digastric.

Passing along the mandibular canal, the inferior alveolar nerve gives off branches that supply the lower teeth and gums. A large branch, the mental nerve, emerges through the mental foramen, which is here. The mental nerve supplies the chin and the lower lip.

Now we'll look at the lingual nerve. To follow it, we'll first remove the inferior alveolar nerve, and the buccinator muscle. This brings us into the oral cavity. The lingual nerve passes close to the mandible. To follow its course, we'll remove this part of the mandible.

We'll also remove the mucosa from the side of the tongue, and the floor of the mouth. Here's the lingual nerve. Now that we can see it all, we'll follow it from the top.

Up here the divided stump of the inferior alveolar nerve has been displaced forward so that we can see an important detail. Early in its course the lingual nerve is joined by this nerve, the chorda tympani, which is a special branch of the facial nerve. The lingual nerve runs down toward the corner of the medial pterygoid muscle, passing just medial to the buttress of the mandible.

The lingual nerve passes forwards along the base of the tongue, giving off branches along its length. The lingual nerve provides common sensation, and also taste sensation, to the anterior two-thirds of the tongue. The taste fibers that travel in the lingual nerve are carried by the chorda tympani.