88 Journal of Comparative Neurology and Psychology. 



receives impressions of non-splanchnic character which are not in 

 immediate relation with the viscera. 



Though I could not control by personal examination the 

 published data about the peripheral distribution of the different 

 sensory nerves of this region, yet I willingly acknowledge that 

 during my examination at first undertaken in a rather skeptical 

 spirit in this matter, I never met with any fact which I might 

 advance against the opinions of the American school. The truth 

 lies rather on the other side. I consider the conclusions of this 

 school and the methods of investigation by which Strong, 

 Kingsbury, Herrick and Johnston reached their conclusions 

 about the microscopic structure of the centers and the peripheral 

 courses of the nerves as necessary to complete the interesting and 

 excellent work which Burckhardt began in the selachians of 

 getting by the microscopical method a better insight into the 

 problem how the medulla oblongata has developed from the 

 medulla spinalis. 



2. The Hind-brain of the Selachians. 



The hind-brain of the sharks is distinguished by its form in 

 some very important respects from that of the teleosts. The 

 velum anticum cerebelli in the teleosts is more voluminous than 

 in the selachians, this difference being very great between Galeus 

 and Gadus. While in the latter fish the velum has a large dorso- 

 ventral dimension and not only contains tracts, but is richly 

 supplied with gray substance which is directly continuous with the 

 nucleus lateralis cerebelli, we find this region in Galeus to consist 

 only of a relatively smaller number of decussating medullated 

 fibers, as shown in Figs. Ixx and Ixxiii, Plate IV. 



While in the codfish the strongly developed tr. mesencephalo- 

 cerebellaris runs through this velum and the valvula cerebelli 

 itself has a very broad attachment to it, we find in the same part 

 of the brain in Galeus and Angelus squatina only the much 

 smaller upper tecto-cerebellar tract. The lateral nucleus, which 

 in the teleosts is the direct backward continuation of the velum, 

 is smaller here and lies farther backward in the lateral arms of 

 the cerebellum (Figs. Hi to Ixxiii). 



It is chiefly this last factor, the fact that this nervous mass 

 projects inward very much less, that explains why in the sharks 



