xin PHYLUM CHORDATA 161 



the snout.i The main trunk of the nerve then runs forwards and 

 outwards across the floor of the orbit, and divides into two branches, 

 the maxillary and mandibular, or second and third divisions of the 

 trigeminal. The former {mx. V) supplies the skin of the ventral 

 surface of the snout, the latter {mnd. V) the skin and muscles 

 of the lower jaw. 



Of the branches of the facial, the ophthalmic runs through the 

 orbit in close relation to the superficial ophthalmic branch of the 

 trigeminal, and is distributed to the sensory and ampullary 

 canals of the snout region ; the buccal runs forwards in intimate 

 relation with the maxillary division of the trigeminal, and breaks 

 up into branches which are distributed to the sensory canals and 

 ampuUc-e of the region of the snout ; the palatine {pi. VII, Flip.) 

 runs to the roof of the mouth ; the main body of the nerve — 

 hyomandibular nerve (%. mnd. VII, Vllhy.) — then runs outwards 

 close to the edge of the hyomandibular cartilage and behind the 

 spiracle, eventually becoming distributed to the muscles between 

 the spiracle and the first branchial cleft : a small external mandi- 

 bular branch (VlI.e.m.) comes off from it and goes to the lateral 

 and ampullary canals of the lower jaw. 



The eighth or auditory nerve passes directly into the internal 

 ear, and breaks up into branches for the supply of its various 

 parts. The glossopharyngeal (gl. ph. IZ.) perforates the posterior 

 part of the auditory region of the skull, and, after it reaches the 

 exterior, passes to the first branchial cleft, where it bifurcates, one 

 branch passing to the anterior, and the other to the posterior 

 wall of the cleft. The last nerve of the series — the fneumogastric or 

 vagus {vag., ^)^is a large nerve which emerges from the skull by 

 an aperture situated between the auditory region and the foramen 

 magnum. It first gives off a series of four branchial branches, each 

 of which bifurcates to supply the anterior and posterior borders of 

 the last four branchial clefts. The lateralis nerve {lat. vag., X.l.) 

 is usually referred to as a branch of the vagus since it runs in 

 intimate connection with the trunk of that nerve for some 

 distance, but it has a distinct origin in the medulla : after becom- 

 ing separated from the vagus trunk it runs along beneath the 

 peritoneum opposite the lateral line, which it supplies, to the 

 posterior end of the body. The rest of the vagus runs backwards 

 to divide into cardiac branches for the heart and gastric branches 

 for the stomach. 



^ In most Elasmobranchs a nerve of considerable size^the ophthalmicus pro- 

 fundus (Fig. 779) arises from the dorsal and anterior part of the Gasserian 

 ganglion, and is usually regarded as a branch of the trigeminal. It runs forwards 

 over the external rectus muscle and under the superior rectus, and perforates 

 the pre-orbital process to end in the integument of the snout. Among other 

 branches it gives off ciliary branches to the iris : these are joined by the ciliary 

 branches of the oculomotor. An ophthalmicus profundus is not present in 

 Soyllium in the adult condition. 



VtW. IT Jj 



