This is much the largest of the cranial nerves, and the variety and importance of its functions imbue it with more than ordinary interest.
To commence with, it possesses (1) a sensory and (2) a motor root. The sensory root springs from the anterior part of the pons varolii, and has upon it a large elongated body, the Gasserian ganglion. From this spring three branches, termed respectively the ophthalmic, superior maxillary, and inferior maxillary nerves.
The motor root is the smaller of the two, and is situated on the inner side of the longer one, with which it takes origin from the pons varolii. From this point it proceeds forward to unite with the inferior maxillary nerve, which is now both sensitive and motor.
The superior maxillary division is the largest of the several branches of this nerve; it leaves the cranium through the foramen rotundum. The ophthalmic, which is the smallest, passes out by the foramen lacerum orbitale, and the inferior maxillary division by the anterior opening in the foramen lacerum basis cranii.
On emerging from these openings the ophthalmic branch gives off -
1. The Frontal or Supra-Orbital after emerging from the supra-orbital foramen is distributed to the skin of the forehead and the upper eyelid.
2. The Lachrymal Nerve to the lachrymal gland and the muscles and skin of the ear.
3. The Palpebro-Nasal Nerve to the inner angle of the eye, the lachrymal apparatus, and the lower eyelid. It also supplies the membrana nictitans, and sends a branch to the sensitive roots of the ophthalmic ganglion.
The Superior Maxillary Nerve emerges from the cranium at the foramen rotundum and enters the superior dental canal. It gives off, among others -
1. The Orbital branch to the eyelids and skin.
2. Great Anterior or Palatine Nerve traverses the palatine canal and is distributed to the hard palate and gums.
3. The Staphyline or Posterior Palatine Nerve to the velum palati and soft palate.
4. Nasal or Spheno-Palatine Nerve to the mucous membrane of the nose.
5. The Dental Nerve to the superior molar, incisor, and canine teeth.
The Inferior Maxillary Nerve, as we have already pointed out, contains both sensory and motor filaments. It gives off -
1. The Masseteric Nerve, to the masseter and temporal muscles.
2. The Buccal Nerve, to the external pterygoid muscle, to the orbital portion of the temporal muscle, the molar glands, the buccinator muscle, and to the lips.
3. Nerve of Internal Pterygoid Muscle, to the internal pterygoid muscle.
4. Superficial Temporal or Subzygomatic Nerve furnishes small filaments to the guttural pouch and the parotid gland. It sends a branch to join the seventh nerve as it passes on to the face.
5. The Gustatory Nerve, the larger of the branches of the inferior maxillary trunk, is distributed to the mucous membrane of the tongue, and the sublingual and submaxillary glands. This is the nerve of taste. It is joined near its origin by the chorda tympani, a branch of the facial nerve.
7. The inferior Dental Nerve enters the dental canal in the inferior maxillary bone, and gives sensory branches to the teeth.
8. The Mental Nerve to the lower lip.