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principal trunk of tlie facial leaves the skull by a circular foramen in the prootic bone, 

 and then passes through a foramen in the head of the hyomandibular. But after this 

 it is still covered by the preoperculura, which must be removed before the distribution 

 of the nerve can be observed : the facial runs for some distance between the 

 hyomandibular and the preoperculum. Soon after its exit from the hyomandibular 

 foramen the nerve trunk divides into two branches, the posterior of which is the 

 ramus operadaris, the anterior the ramus hyoideo-)nandibularis. The ramus opercidaris 

 (VII 2a, PI. XV, 2) divides into branches which are distributed to the skm of the 

 operculum. The ramus hyoideo-ma^idibularis divides into two branches, one of which, 

 the rarmis mandibidaris, VII 1, runs along the anterior part of the surface of the 

 quadrate. It gives off branches to the jaw-muscle, and into the substance of the 

 quadrate, and passes through a foramen in the head of the quadrate to the inner side 

 of the mandibular bone, where it supplies the transverse mandibular muscle, the genio- 

 hyoid muscle, and the mucous membrane of the floor of the mouth. The other branch, 

 the ramus liyoideus, VII 2, bends inwards to reach the inner side of the stylohyal 

 bone, and is distributed to the inner surface of the hyoid arch. 



The eighth cranial nerve is the auditory, which never leaves the interior of the skuU, 

 but is exclusively distributed to the auditory organ : it is the auditory nerve. 



The ninth cranial nerve is called the glosso-pharyngeal, a name taken from human 

 anatomy, but not at all appropriate to the anatomy of fishes. This nerve, like the 

 seventh, is distributed in the same way on each side. It makes its exit from the skull 

 by a special small foramen in the opisthotic bone, arising from the medulla oblongata 

 by an independent root. On the trunk of the nerve, a little beyond its exit from the 

 skull, there is a ganglion of considerable size, below which the nerve bifurcates into 

 two branches. The anterior branch goes to the posterior surface of the operculum 

 and hyoid arch, the posterior to the anterior surface of the first branchial arch. 



The tenth cranial nerve, called nervus vagus, is more widely distributed than any 

 of the others, and represents a series of nerves united into a common trunk at their 

 origin. The single trunk passes out of the skull through a circular foramen in the 

 exoccipital bone, and then divides into several branches. The first branch, the most 

 anterior, bifurcates into two, and has a large ganglion at the point of bifurcation ; 

 it forks over the second branchial cleft, the front branch going to the posterior face of 

 the first branchial arch, the posterior branch to the anterior face of the second 

 branchial arch. Similarly the second branch of the vagus bifurcates over the third 

 branchial cleft, and has a ganglion at its point of bifurcation. The third branch has 

 no ganglion, but bifurcates in the same way over the fourth branchial cleft. The 

 fourth branch bifurcates over the fifth branchial cleft, its anterior branch going to the 

 posterior face of the fourth branchial arch, its posterior branch to the posterior wall of 

 the branchial chamber and the fifth branchial arch. A nerve from this branch goes 

 to the heart. The fifth branch of the vagus runs down the oesophagus to the stomach. 

 The sixth branch is the lateral nerve or nerve of the lateral line : it runs close above 



