254 NERVE COMPONENTS OF BONY FISHES. 



fibres properly its own." This view is not without opponents. Onuf 

 and Collins ('98) find degenerations after extirpation of sympathetic 

 ganglia which they can explain on.no other assumption than that of 

 sensory fibres running from cells of the sympathetic ganglia into the 

 dorsal roots. 



But leaving the question of the sympathetic connections to one 

 side, we have the most abundant evidence (see e. g.. Thane, '95, 

 p. 350, KoUiker, '96, p. 858, and Huber, '97, p. 131) that sensory 

 cerebro-spinal fibres distribute freely among all of the viscera through 

 the mediation of the sympathetic nerves. The findings of experi- 

 mental phj^siology and pathology also necessitate the assumption of 

 such fibres in order to explain the phenomena of the reflexes, etc. 

 Where the spinal centres for these visceral fibres may be has not been 

 accurately determined, but the presumption, it seems to me, is 

 rather in favor of than against the idea that they are distinct from 

 the general cutaneous centres. It is, undoubtedly, true that this 

 spinal viscero-sensory system is very small and that it is not present 

 in all of the spinal segments is very probable ; for, as we have seen, 

 the functions of this system have been very largely usurped by the 

 cranial visceral system of the vagus. 



Passing now to the head, the presence of the branchial 

 apparatus and the reduction of the somatic musculature 

 have so modified the conditions as to render comparison 

 v^ith the trunk almost impossible. If we exclude the 

 twelfth cranial, which in the fishes is but little modified 

 from the typical spinals, there is no cranial nerve which 

 has a ventral ramus of the typical form. The reason is 

 clear. There is no ventral somatic musculature in the 

 head aside from that which has grown forward from 

 the region of the first spinal. And in the higher 

 fishes the overgrowth of the operculum has eliminated 

 in the branchial region the cutaneous areas which would 

 be innervated from ventral spinal rami. It would be 

 interesting to learn in the sharks the exact details of 

 the innervation of the skin of the venter in the gill 

 region. The branchial trunk is commonly supposed to 

 represent a ventral ramus. Whether this is so can only 

 be determined positively after a more careful examination 



