30 ELEMENTARY BIOLOGY. [CHAP. 



into two branches which enter the auditory capsule to 

 reach the organ of hearing. 



The Post-auditory nerves are : 



9. The Glossopharyngei. 



These nerves arise, side by side with the next, from 

 the medulla oblongata; and the roots of both leave 

 the skull by an aperture behind the auditory capsule 

 on each side, and form a common ganglion. Each 

 passes downwards and forwards to the root of the 

 tongue, which organ it finally supplies. Moreover, it 

 gives off muscular branches and forms an anastomo- 

 sis with the seventh. 



10. The Pneumogastrici or Vagi. 



Immediately after leaving the ganglia these nerves 

 separate from the glossopharyngeal and each gives 

 off a cutaneous branch to the dorsal integument of 

 the head and trunk : it then divides into two 

 branches, one of which is distributed to the larynx, 

 the other to the heart, lungs, and stomach. (Sym- 

 pathetic fibres are in part bound up with these.) 



The myelon or spinal cord is continued back from the 

 hind-brain as a subcylindrical cord, which lessens somewhat 

 rapidly towards its apparent end at the level of the seventh 

 vertebra. It does not really end here, however, but is con- 

 tinued back as a slender filament, the filum terminale, to the 

 commencement of the canal of the urostyle. The diameter 

 of the cord is somewhat enlarged opposite the origin of the 

 nerves for the limbs. In transverse sections, the cord is 

 seen to be not truly cylindrical but to be indented by 

 two longitudinal grooves, one dorsal and one ventral, which 

 leave but a small connecting bridge between its two halves. 



