CRANIAL NERVES 149 



bility into physiological relation is at the bulbo-spinal junction 

 (chap. ix). 



The preceding analysis illustrates the intimate physiological rela- 

 tionship which exists among the various modalities of sense which 

 may be concerned with the resolution of mixed sensory experience in 

 the interest of securing the appropriate responses. The integrating 

 apparatus is spread from the peripheral end-organs throughout the 

 central nervous system. Within this machinery for conjoint action 

 there have been differentiated the specific sensory and motor sys- 

 tems, that is, the analyzers. The first step in this analysis is the sepa- 

 ration in the central adjustors of the visceral from the somatic sys- 

 tems. Thus the fibers of taste and general visceral sensibility converge 

 into the f. solitarius, well separated from all the somatic sensory 

 systems which are assembled more superficially. This segregation 

 obviously has arisen because of the radical differences in the courses 

 taken by the efferent fibers from visceral and somatic receptive fields 

 to visceral and somatic effectors, respectively. 



In general, the gustatory fibers tend to end near their entrance into 

 the brain, and the general visceral fibers to descend toward the lower 

 end of the system. In elasmobranchs the nucleus of the f . solitarius is 

 locally enlarged, with a separate lobe for each of the nerves of the 

 gills. These enlargements, which show as a beadlike row in the wall of 

 the fourth ventricle, are probably chiefly gustatory. In the carp and 

 some other teleosts with enormous numbers of taste buds, there are 

 separate enlargements of this nucleus known as facial, glossopharyn- 

 geal, and vagal lobes. These are known to be largely gustatory in 

 function. In other species of teleosts there are various modifications 

 of these arrangements. In some birds with very few taste buds the 

 f . solitarius is clearly double. A very slender medial bundle carries the 

 few gustatory fibers and the much larger lateral bundle, the general 

 visceral fibers (Ariens Kappers, Huber, Crosby, '36, p. 370). In 

 Amblystoma, as in mammals,. none of these specializations have oc- 

 curred, and the visceral sensory system as a whole retains its primi- 

 tive characteristics. 



SOMATIC MOTOR NERVE ROOTS 



These roots in Amblystoma comprise only fibers for the extrinsic 

 muscles of the eyeball in the roots of the III, IV, and VI nerves. As 

 previously mentioned, all peripheral motor neurons are mingled with 



