20 NERVOUS SYSTEM OF VERTEBRATES. 



ramus pharyngeus to the mucosa of the roof of the pharynx, and 

 then supplies the gill filaments and the mucosa of the lateral 

 and ventral walls of the pharynx. The other is the ramus post- 

 trematicus which runs ventrally behind the gill slit and supplies 

 the muscles of the branchial arch, gill filaments, the mucosa and 

 taste buds, and in cyclostomes the overlying skin. Beyond the 

 last gill slit the vagus trunk is continued caudad as the ramus 

 intestinalis. In many forms especially among bony fishes the 

 position of the roots and ganglia of the vagus with reference to 

 the gills becomes modified and is not so simple as indicated in 

 the diagram. Figures 51, 63, 79 will show the arrangement in a 

 cyclostome, a bony fish and an amphibian. 



The more caudal motor roots of the vagus series supply certain 

 muscles* connected with the shoulder girdle (trapezius muscula- 

 ture). Owing to the disappearance of the gills in higher verte- 

 brates and the consequent reduction of the more cephalic motor 

 roots, these more caudal roots become more prominent higher in 

 the scale of vertebrates. They have been set apart as an inde- 

 pendent nerve under the name of the eleventh cranial or spinal 

 accessory nerve. 



A short distance cephalad from the vagus appears the ninth 

 cranial or glossn pharyngeus nerve. It arises by a sensory and a 

 motor root, bears a ganglion over the first gill slit, and gives rise 

 to pharyngeal, pretrematic and posttrematic rami as in the case 

 of each of the vagus ganglia. The pharyngeal ramus extends 

 into the palate and is known as the ramus palatinus IX, and the 

 posttrematic ramus is known as the ramus lingualis IX because 

 it continues into the tongue. 



Above the glossopharyngeus, sometimes in front of and sometimes 

 behind it, arises the nervus lineae later alls. It is an independent 

 sensory root which usually joins the trunk of the vagus and runs 

 for some distance with it, then continues separately beneath the 

 skin as the nerve of the special sense organs of the lateral line. 

 This nerve enters the dorsal somatic sensory lobe and cephalad 

 from it two or three other roots enter the same lobe. The most 

 caudal of these is the eighth cranial or auditory nerve. In front 

 of this there are in cyclostomes, selachians and ganoids, two 



