XIII PHYLUM CHORDATA 105 



the fonnor present in Fishes only : the latter in some Fishes a 

 semi-independent nerve given otf separately from the dorsal part 

 of the trigeminal ganglion. The ophthalmic is purely sensory, and 

 supplies the skin in the neighbourhood of the mouth and certain 

 parts in the orbit. The maciUarn nerve (V. mx.) is also sensory: 

 it supplies the parts in relation with the upper jaw, including the 

 teeth. The mandihular nerve (V, mcl.) is partly sensory, partly 

 motor : it supplies the muscles of the jaws, the skin and teeth of 

 the lower jaw, and sends off a g'nstatory nerve or nerve of taste to 

 the epithelium of the tongue in the higher forms. The ophthalmic 

 nerve is connected by a branch with the ciliary ganglion. 



The sicdh or ahducent (Figs. 779 and 787, VI.) is a small motor 

 nerve, arising from the ventral region of the medulla, and sup- 

 plying the external rectus muscle of the eye. We thus have the 

 remarkable fact that out of ten, or at the most twelve, cerebral 

 nerves, three are devoted to the supply of the six small muscles 

 by which the eye-ball is moved, and of those by which the 

 accommodation of the eye for varying distances is effected. 



The seventh or faeial (Fig. 779, VII.) is, like the fifth, a mixed 

 nerve in the lower Craniata, i.e., contains both sensory and motor 

 fibres. It arises from the side of the medulla, a short distance 

 behind the fifth, and is dilated near its origin into o, facial ganglion. 

 It has two chief branches, a imlatine (VII. p.), which passes in 

 front of the mandibulo-h3'oid gill-cleft, and supplies the mucous 

 membrane of the palate, and a hyomandihular (VII. h.), which 

 passes behind the same cleft and sends branches to the lower 

 jaw and to the hyoid arch. In most aquatic Vertebrata an 

 ophthalmic branch is given off from the trunk of the nerve, and 

 usually accompanies the superficial ophthalmic division of the 

 fifth. In the higher Vertebrata the seventh becomes a purely 

 motor nerve, supplying the muscles of the face. 



The eighth or auditory nerve (VIII.) arises immediately behind 

 the seventh, with which it is intimately connected at its origin. 

 It is a purely sensory nerve, supplying the organ of hearing, ^'.c.,the 

 epithelium of the membranous labyrinth presently to be 

 described. 



The ninth or glossop)haryngeal (IX.) is a mixed nerve : it arises 

 from the lateral region of the medulla, behind the organ of 

 hearing, and is connected at its origin with the vagus ganglion 

 (see below). Its trunk passes downwards and forks over the 

 second gill-cleft, sending an anterior branch to the hyoid arch 

 which bounds the cleft in front, and a posterior branch to the first 

 branchial arch which bounds it posteriorly. Thus the entire 

 nerve supplies the second gill-pouch, including both branchial 

 filaments and muscles : its anterior branch goes to the posterior 

 heinibranch of the hyoid arch, its posterior branch to the anterior 

 hemibranch of the first branchial arch. In the air-breathing 



