CRANIAL NERVES 38 I 



pre-iranchial nerve (visceral sensory), skirting tlie anterior 

 margin of a cleft in its ventral course ; and (7) a post-branchial 

 branch (visceral motor) similarly related to the hinder margin. 



The first six cranial nerves resemble those of the higher 

 Craniates in their mode of origin from the brain, in the physio- 

 logical nature of their component fibres, and in their peripheral 

 distribution, and therefore they need not be specially referred to 

 here. ' The principal branches of the fifth or trigeminal nerve 

 are shown in Fig. 218. Comparing this nerve with a typical 

 branchial nerve it would seem that the profundus and super- 

 ficialis ophthalmic nerves are dorsal nerves ; the maxillaris and 

 ■mandilndnris, pre- and post-branchial branches, respectively, in 

 relation with the modified gill-cleft which forms the mouth, 

 while the branch to the oral surface represents a palatine nerve. 

 The most important of the distinctive features in the cranial 

 nerves of Fishes are to be found in the relations of nerves vii., ix., 

 and X. to branchial clefts, and in the lateralis system of nerve 

 components and its association with the lateral line sensory 

 organs. The seventh or facial nerve is an exceptionally interest- 

 ing nerve. Besides the usual components of a typical branchial 

 nerve certain of its so-called branches are wholly or largely 

 derived from the lateralis system. For this reason the nerve 

 may be said to consist of two portions, the facial proper, or 

 those fibres which constitute the facial nerve in air-breathing 

 Craniates, and the lateralis branches which solely innervate 

 lateral line sense-organs, and are therefore peculiar to aquatic 

 forms. The facial proper has a ganglion (the facial or geni- 

 culate ganglion) on its root, and on entering the orbit after 

 traversing the cranial wall it gives off a palatine nerve. Just 

 over the spiracle a pre-branchicd nerve, the representative of the 

 chorda tympani of Mammals, leaves the main trunk, and passes 

 ventrally in relation with the anterior wall of the spiracle to 

 its ultimate distribution in the walls of the mouth cavity. 

 The main trunk, now called the ramus hyomandibidaris, 

 then pursues a ventral course behind the spiracle as a 

 post-branchial nerve, and certain of its mainly motor branches 

 which pass downwards in connexion with the hyoid arch 

 supply the muscles of that arch, and, if an operculum 

 is present, the opercular muscles as well. The lateralis 

 portion of the facial includes the following principal branches, 



