264 NERVE COMPONENTS OF BONY FISHES. 



The general result of the study is to demonstrate that it 

 is possible, even in forms so highly specialized as the 

 teleosts, to trace in serial sections the entire courses of 

 the chief sensory and motor components of the cranial 

 nerves and that the results of such an analysis show a 

 striking fundamental agreement in the plan of the nervous 

 system with the Amphibia, as worked out by Strong. 

 This plan, in its main outlines, seems to be a palingenetic 

 character of great constancy throughout the vertebrates. 

 As in the Amphibia, the sensory components of the cranial 

 nerves, to which attention has been especially directed, 

 fall into three categories, each with its distinct terminal 

 nuclei within the brain, roots, ganglia and peripheral 

 branches. The latter, however, may be secondarily fused 

 and modified in a great variety of ways, so that the periph- 

 eral nerves, as commonly named, do not usually bear a 

 simple relation to the roots and ganglia from which they 

 arise ; much less can they be regarded as simple metameric 

 units. 



On the contrary, each of the sensory cranial systems has 

 been, for physiological reasons, unified and concentrated 

 in the medulla oblongata, and in consequence of this, it 

 has come to be represented in the nerves of but few of the 

 segments, either having been lost or not having been 

 differentiated in the others. Thus it happens that any 

 peripheral ramus may be composed of elements which are 

 not only very diverse functionally, but which ma)^ have 

 belonged primitively to different metameres. 



Of these systems the general cutaneous is probably the 

 oldest phylogenetically. It has been subjected to very 

 slight modification in the head as compared with its 

 arrangement in the spinal nerves, though it is represented 

 in the V and X nerves only. 



