202 STRONG. [Vol. X. 



a N. lateralis ventralis, and a N. visceralis. Only the latter 

 contains motor as well as sensory fibres (motor to the splanch- 

 nic muscles). This primitive relation is retained by the cranial 

 nerves, and the loss of this relation and of certain branches 

 by the spinal nerves is owing to the usurpation of the 

 long trunk-branches of the cranial nerves. The course of the 

 spinal dorsal nerves inside the body muscles he regards as due 

 to the shortening of the dorsal nerve. Kupffer, however, 

 regards the spinal dorsal nerve as a new acquisition. This 

 peculiarity presented by the spinal nerves is very important, 

 and its satisfactory explanation must be a crucial point in any 

 theory of the cranial and spinal nerves. 



Two general criticisms that may be made upon Hatschek's 

 views, I think, are that they do not take sufficiently into 

 account qualitative differences in the nerves under discussion, 

 his conclusions being based more upon simply topographical 

 relations, and, secondly, that they consider the nerves too much 

 apart from correlated structures, from those innervated by them 

 especially, and, consequently, offer no explanation why the 

 usurpation in question took place. 



We have seen that in the cranial nerves of the higher fishes 

 there are three kinds of cutaneous nerves distinguishable by 

 peculiarities of their fibres, of their distribution, and of their 

 internal origin, i.e., (i) mixed fibres of a general cutaneous 

 character continuous with the posterior columns of the cord, 

 (2) coarse fibres innervating the lateral line organs and ter- 

 minating centrally in the differentiated tuberculum acusticum, 

 and (3) fine fibres innervating the terminal buds (coarse in 

 Selachians and innervating the ampullae .-*) and terminating 

 centrally (principally) in the lobus trigemini. The latter, i.e.y 

 (3), is possibly not completely differentiated. Among the 

 Cyclostomes, it seems probable, this specialization has not been 

 carried so far, but this is not yet sufficiently known. 



It is obvious that it is only similar and specialized structures 

 that are most likely to attain a more unified innervation, and, 

 accordingly, it seems most probable that such a process of 

 usurpation as that mentioned above would take place in con- 

 nection with the cutaneous sense organs. These latter would 



