xiii PHYLUM CHORDATA 149 



the ' general origin and distribution which has already been 

 described as universal in the Craniata (p. 97). 



The trigeminal (Fig. 775, V) arises in close relation to the 

 facial. As it passes into the orbit it swells into a ganglion the 

 Gasserian. Its chief branches are three in number. The first 

 given off is the superficial ophthalmic (Fig. 777, oph. V), which runs 

 forwards through the orbit above the origin of the recti muscles, 

 and in very close relation with the ophthalmic branch of the facial. 

 Anteriority it breaks up into branches for the supply of the mucous 

 canals of the dorsal surface of the snout. 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 mucous canals of the ventral surface of the 

 snout ; the latter (mnd.V) supplies the muscles of the lower jaw. 



A nerve of considerable size, the cpMhalmicus profundus 

 arises in front of the root of the trigeminal, with which it is 

 in close communication. After leaving the cranial cavity it 

 enlarges into a small ganglion, and 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. 



Of the branches of the facial, the superficial ophthalmic runs 

 through the orbit in close relation to the superficial ophthalmic 

 branch of the trigeminal, and is distributed to the ampullae and 

 mucous 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 mainly distributed to the 

 ampulla? and canals of the region of the snout ; the palatine 

 (pi. VII) runs to the roof of the mouth; the main body of the 

 nerve hyomandibular nerve (hy. mnd. VII) 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. 



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.) 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 pneumogastric 

 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. It then gives off a lateral nerve 



