FIFTH NERVE, the chief sensory nerve of the face, also called trigeminu.s, or trifadal. It is one of the fifth cranial pair of nerves. The fifth nerve is one of the most important sensory nerves of the body, its name trafacial meaning that it has three large divisions which are distributed to the face, and its name tri geminus being given because it has three roots inside the skull. It is really a mixed nerve containing both motor and sensory fibres. The motor root rises from a group of cells lying deep in the floor of the fourth ventricle. The sensory portion arises in a series of ganglia, the Gasserian ganglion being the most important one. The ophthalmic and Meckel's ganglia are also smaller ganglionic centres. The chief branches go to supply the entire area of the skin of the face and head, and netiralgias and nenritides of the face and head are due to affections of this nerve. The chief division is the first or ophthalmic division, which supplies the region over the superior surface of the nose, forehead and eye, running as far back as the top of the head. The second branch is the
superior maxillary, which supplies the tooth and the region of the skin beneath the orbit, the upper lip, and the region of the temple. The superior maxillary nerve contains a few motor fibres. The third branch, the interior maxillary, or mandibular, is the largest branch of the fifth nerve, and contains most of the motor fibres. It supplies the surface of the skin of the lower jaw, front of the ear, and temporal region, lying close behind the area supplied by the maxillary. The muscles of the jaw, the masseters, tem porals and buccinators are supplied by the motor fibres of this branch. See CRANIAL NERVES ; FACIAL NEURALGIA ; NEURALGIA.