4 



of course, bat ratninin^^, with'il, nuch of tha archnic nervous 

 or^-iai nation from ivhich higher braius have been griiually evolv- 

 ed. A study of such a simple brain as that of a selachian con- 

 stitutes, therefore, a necessary introduction to the more highly 

 differentiated nervous systems of birds and manmals. 



Our kno/fleige of the nervous system is so peculiarly de- 

 pendent upon methods of investigation that the conceptions held 

 by us might almost be said to grow out of the teohnique employ- 

 ed. 'The development of neurological methods daring the last 

 few years has been indeed phenomenal, and with this advance 

 there has come the necessity for a re-investigation of many 

 nervous systems. The results obtained by the earlier observers, 

 while praiseworthy in themselves, siicply do not furnish the pre- 

 cise and complete pictures of neurones which modern comparative 

 neurology requires. And hence it is that the writer has attack- 

 ed anew the structural problems of a brain which has by no means 

 escaped the attention of investigators. The phylogenetic value 

 usually assigned to the Selachii has caused many to examine 

 the brain of the shark, both anatomically and microscopically. 

 A historical review of the latter class of researches will be 

 found in Section I[, 2. 



The results set forth in this paper are intended to farther 

 exact knowledge concerning the external morphology, the internal 

 organisation, and the architectural relations of the selachian 

 neurones, while also aiding, it is hoped, in the elucidation of 

 certain questions of a general character. The particular sela- 



