_Trigeminus_ (V.).--The _ophthalmicus profundus_ branch (op.p.)--which probably is morphologically a distinct cranial nerve--passes forwards along the roof of the orbit to the skin of the snout. As it passes through the orbit it gives off the long ciliary nerves to the eyeball, and is connected with the small ciliary ganglion (also connected with III.) which in turn gives off the short ciliary nerves to the eyeball. The _ophthalmicus superficialis_ (cut short in the figure) branch passes from the root ganglion of V. (Gasserian ganglion), and passes also over the orbit to the skin of the snout. It lies close to, or completely fused with, the corresponding branch of the lateralis system. The main trunk of V. branches over the edge of the mouth into the _maxillary_ (mx.) and _mandibular_ (md.) divisions, the former, like the two branches already mentioned, purely sensory, the latter mixed--supplying the muscles of mastication as well as the teeth of the lower jaw and the lining of the buccal floor. The main trunk of the _Facialis_ (VII.) bifurcates over the spiracle into a pre-spiracular portion--the main portion of which passes to the mucous membrane of the palate as the palatine (pnVII.)--and a postspiracular portion, the hyomandibular (hy.) trunk which supplies the muscles of the hyoid arch and also sends a few sensory fibres to the lining of the spiracle, the floor of mouth and pharynx and the skin of the lower jaw. Combined with the main trunk of the facial are branches belonging to the _lateralis_ system. _Lateralis Group of Nerves._--The _lateralis_ group of nerves are charged with the innervation of the system of cutaneous sense organs and are all connected with the same central region in the medulla. A special sensory area of the ectoderm becomes involuted below the surface to form the otocyst, and the nerve fibres belonging to this form the auditory nerve (VIII.). Other portions of the _lateralis_ group become mixed up with various other cranial nerves as follows: (a) Facial portion. (1) _Ophthalmicus superficialis_ (op.s.VII.): passes to lining of nose or to the lateral line organs of the dorsal part of snout. (2) _Buccal_ (bucc.VII): lies close to maxillary division of V. and passes to the sensory canals of the lower side of the snout. (3) _External mandibular_ (md.ex.): lies in close association with the mandibular division of V., supplies the sensory canals of the lower jaw and hyoid region. _Lateralis vagi_ (l.n.X.) becomes closely associated with the vagus. It supplies the lateral line organs of the trunk. In the lamprey and in Dipnoans the _lateralis vagi_ loses its superficial position in the adult and comes into close relation with the notochord.