138 SUB-CLASS ELASMOBRAXCHII. 



those of the trigemino -facial group and is distributed to the 

 walls of the otocyst. 



The glossopharyngeal {G'p) arises just in front of the vagus by 

 three or four rootlets. It passes out by a canal below the audi- 

 tory capsule, dilates into a ganglion and gives off a small dorsal 

 nerve which in some cases is said to supply a part of the cephalic 

 lateral line. The nerve continues to the first branchial arch 

 giving off a prebranchial branch to the hyoid and a pharyngeal 

 branch. 



In the vagus the root of the lateral line nerve {lateralis) must 

 be distinguished from the roots of the rest of the nerve. The 

 lateralis nerve {In) arises by a root dorsal to and slightly in front 

 of the glossopharyngeal. It leaves the skull with the rest of the 

 vagus to which it is closely applied and dilates into a ganglion. 

 It is continued to the end of the body and supplies the trunk 

 portion of the lateral line canal, and a small portion of the cranial 

 lateral line. The remaining vagus roots, which are numerous, 

 unite to form five nerves each of which has a ganglion. These 

 are at first closely connected together and are distributed in the 

 typical manner, the first four to the four hinder branchial arches 

 and the last is continued as the intestinal branch (m). 



A variable number of anterior roots of spinal nerves * of which 

 the posterior roots though present in the embryo are absent in 

 the adult, arise from the medulla ventral to the vagus roots. 

 They were formerly mistaken by Gegenbaur for ventral roots of 

 the vagus and were called ventral vagus roots. They are absent 

 in some Raji. They leave the skull wall by special foramina in 

 the occipital region and innervate some muscles of the fore-limb 

 and some ventral branchial muscles. They are called the spino- 

 occipital nerves. 



It has been shown in Amphibia that the superficial ophthalmic 

 of the facial, the buccal and external mandibular of the facial 

 and the lateralis of the vagus arise from the acustico-lateralis 

 nucleus in the brain (see p. 75). All these nerves are developed 

 from the surface ectoderm and sink inwards to their adult posi- 

 tions and when in Amphibia the lateral line sense organs dis- 

 appear the whole of these nerves disappear also. 



* M. FLirbriager, Ueh. d. S'pino-occipitalen Nerven der Selachier, etc., 

 Leipzig, 1897. 



