xxviii Journal of Comparative Neurology. 



neurologists, a portion of them are here repeated. The introductory 

 and concluding sections are given nearly entire and the summaries of 

 the others. Only the more important of the experiments which gave 

 positive results are reprinted, but those which are given are numbered 

 as in the original paper. 



The writer has been engaged for several months upon an investi- 

 gation, which is still incomplete, of the components of the cranial 

 nerves of the bony fishes. This research has involved the reconstruc- 

 tion from serial sections of the entire courses of the cranial nerves from 

 their nuclei of origin or termination in the brain to their peripheral 

 termini. Upon plots of the cranial nerves, as thus reconstructed, the 

 components of each nerve have been entered, each component having 

 been followed, so far as possible, through the entire course of the nerve 

 from central origin to peripheral end-organ. 



Proximally the components are for the most part easily recognized 

 from the nuclei of the brain with which they are related ; peripherally 

 the several components of a nerve trunk are again analyzed as they di- 

 verge toward their respective end-organs ; but in their intervening 

 courses the fibers of the several components are so intimately inter- 

 twined that analysis would in most cases be impossible were it not for 

 the fact that the several classes of fibers exhibit well-marked and toler- 

 ably constant differences in their size and the character of their myeli- 

 nation. The fiber-characters of each component are surprisingly simi- 

 lar in all groups of lower vertebrates which have thus far been exam- 

 ined, and the human nerves will, I think, be found also to conform, 

 judging from the rather meager data now available. 



It was in the search for methods adequate for this investigation 

 that the experiments described below were undertaken, and this will 

 explain the rather narrow hmits between which the experiments were 

 confined and in particular why certain procedures favorable for serial 

 section cutting, such as paraffin embedding, were uniformly adhered 

 to. The technical requirements of the case were indeed rather exact- 

 ing, for in order to secure Weigert preparations adapted to the purpose 

 we must have, first, absolutely perfect fixation of the medullary nerve 

 sheaths, far more perfect than is ordinarily given in bichromate of 

 potash preparations. Second, perfectly continuous serial sections must 

 be made through the entire head of the animal under investigation ; for 

 this purpose ribbon cutting after paraffin embedding offers very obvious 

 advantages over the celloidin method. Third, the specimens, though 

 small, should be adult or nearly so, in order that the medullary sheaths 



