i68 



NERVOUS SYSTEM OF VERTEBRATES. 



taste buds by three nerves, the ramus hnguahs IX, the chorda 

 tympani and the ramus hnguahs V. In certain cases in which 

 the Gasserian ganghon was removed and in which the chnical 

 observations were continued for an imusuaUy long time, it was 

 clearly shown that taste was not at all impaired and that the 

 trigeminus provided only for tactile sensation. This is in agree- 

 ment vdth the conditions in lower vertebrates, but it is still possible 

 that taste fibers run in the trigeminus in exceptional cases. The 

 homology of the chorda tympani has been in doubt because it 

 was not certainly known whether the chorda of mammals is a 

 pretrematic or posttrematic ramus. It seems clear now that it 



Fig. 88. — A projection of the cutaneous branches of the communis root of the 

 right facial nerve in a bony fish, Ameiurus. From C. Judson Herrick. All the 

 branches drawn are gustatory in function. Those which supply taste buds within 

 the mouth are not shown. 



is a posttrematic nerve and that the ramus mandibularis VII 

 as seen in the frog tadpole and in fishes is its homologue. The 

 ramus lingualis IX is the homologue of the posttrematic ramus 

 of the IX nerve in fishes and amphibia, which is prolonged into 

 the tongue. 



The taste fibers enter the same centers with the general visceral 

 fibers and no means has yet been discovered of distinguishing 

 between the two. However it is probable that of the two sorts 

 of secondar}' fibers mentioned in the last section, one serves 

 general visceral and the other chiefly gustatory functions. Those 

 which make direct connections with the motor nuclei of the cranial 

 nerves carry only impulses from the visceral surfaces analogous 



