5. The Trigeminal nerve arises from the outer surface of the pons varolii, and passes forward on the base of the skull to the apex of the petrous portion of the temporal bone. There it divides into three trunks :

(1) Ophthalmic-entirely sensory.

(2) Superior maxillary-entirely sensory.

(3) Inferior maxillary-sensory and motor.

(1) The Ophthalmic division passes through the sphenoidal fissure and divides into three branches-{a) lachrymal, (b) frontal, and (c) nasal. The lachrymal nerve passes along the outer side of the orbit and supplies the lachrymal gland, the conjunctiva and skin of the outer corner of the eye. The frontal nerve passes forwards in the upper part of the orbit, and divides into the supraorbital and supratrochlear nerves, which pass through the supraorbital notch and inner corner of the eye respectively, and supply the skin of the forehead and scalp, the supraorbital nerve reaching as far back as the vertex. The nasal nerve enters the nose to supply the mucous membrane, and sends an external branch to supply the skin of the lower part of the nose.

(2) The Superior Maxillary division passes through the foramen rotundum in the root of the pterygoid process, passes through the orbit, and emerges on the face through the infraorbital foramen. Before reaching the face the nerve gives off three dental branches for the supply of the upper teeth, and two branches, the temporal and malar respectively, which emerge from foramina in the malar bone, and supply the skin over that bone and the fore-part of the temple. The infraorbital nerve itself divides into numerous branches, which are arranged in three sets - palpebral for the skin of the lower eyelid, nasal for the skin on the side of the nose, and labial for the skin of the upper lip.

(3) The Inferior Maxillary nerve passes through the foramen ovale in the base of the skull and enters the pterygoid region ; it gives off branches to supply the muscles of mastication-viz., temporal, masseter, internal and external pterygoid, and buccinator. It then gives off five named branches - (a) the buccal, which supplies the skin over the buccinator muscle and the mucous membrane inside the cheek; (b) the auriculotemporal, which supplies the skin over the temple and the scalp just above; (c) the inferior dental, which supplies the lower teeth; (d) the lingual, which supplies the mucous membrane covering the anterior two-thirds of the tongue; (e) the mental, which supplies the skin over the chin.