NERVES OF THE DOGFISH 369 



General cutaneous elements in the vagus of amphibians, with 

 the exception of the caecilians (Norris and Hughes, '18), have 

 long been recognized. 



6. The ramus lateralis X 



This large nerve runs out of the posterior ventral border of the 

 lateral-line ganglion. Its fibers are derived from the second and 

 third divisions of the latter. Its fibers are distributed to the 

 canal organs of the main lateral line and to the series of dorso- 

 lateral pit-organs situated dorsolaterally above the lateral-line 

 canal of the trunk, termed by Johnson ('17) the accessory pit- 

 organs (fig. 50). 



7. The second to the fifth branchial nerves 



The branchial nerves derived from the vagus, in their relations 

 to the branchial clefts and arches are essentially similar to the 

 glossopharyngeal nerve in its relations to the structures of the 

 first branchial cleft and arch. Each nerve may be traced to a 

 distinct root far anterior to its own ganglion, suggesting the elongate 

 root of the ninth. Peripherally to the ganglion each nerve divides 

 into three rami : pharyngeal, pretrematic and posttrematic, with dis- 

 tributions similar to the corresponding rami of the glossopharyngeus. 

 The posttrematic, consisting of a main and a secondary portion, 

 as in the ninth, with similar courses, innervates the corresponding 

 interarcual, adductor arcus branchialis, interbranchial, and ven- 

 tral constrictor muscles. The innervation of the adductor arcus 

 branchialis is in each instance by small nerves that pass through 

 foramina in the epibranchial cartilage. 



The fifth branchial nerve contains only visceral sensory fibers 

 (sympathetic elements being ignored). It leaves the ganglion 

 common to it and the ramus intestinalis farther anteriorly than 

 the latter. After the separation of the other branchial nerves, 

 the fifth continues its position at the ventral mesial border of the 

 ramus intestinalis until it reaches the transverse level of the 

 extreme posterior border of the fourth adductor muscle, where it 

 gives off a ramus posttrematicus. The latter runs posteriorly 



