Fish, Brain of the Fur Seal. » 83 



unless we interpret a slight branch from the cruciate as repre- 

 senting it. In the right hemicerebrums the fissure is distinctly 

 present but is very small. 



The splenial accords more closely with PJioca in its posi- 

 tion, reaching the mid-dorsal region instead of extending farther 

 cephalad as in Callorhinus. It sends off a branch corresponding 

 to the postsplenial as in other brains. 



The presplenial is well represented in the two right hemi- 

 cerebrums, but in the two left it appears to connect the true 

 splenial with the cruciate. The interlocking of submerged but- 

 tresses at the proper points indicates a superficial connection 

 merely. 



The marginal fissure is more poorly developed than in any 

 of the other forms except the bear. A series of short inter- 

 rupted fissures takes its place. 



A well marked collateral fissure is present and resembles 

 the corresponding fissure in CallorJdmis very closely. 



Postcornu. Perhaps the most important point in connect- 

 ing Monachus with Phoea, is a very well developed postcornu. 

 Callorhinus shows the merest trace of one and in the bear it is 

 absent. In Monachus it does not go so far as in Phoca, a 

 great portion of the caudal wall being solid. The floor of the 

 postcornu in Monachus is quite distinctly convex This convex- 

 ity of the internal surface is found to be correlated with an ex- 

 ternal depression, the lower or ventral portion of the splenial 

 fissure. At the more vertical portion of the fissure, namely, 

 opposite the caudal end of the callosum, the splenial fissure 

 loses its totality and and becomes an ordinary fissure for the 

 remainder of its upward course. The postcornu stops at the 

 level of the depth of the splenial fissure in the callosal region. 

 We have not, therefore, as in Phoca, a well developed calcar 

 (hippocamus minor). The internal convex surface already 

 spoken of in connection with the ventral portion of the splenial 

 fissure, offers a suggestion as to the inception of the calcar 

 which finds its fulfillment in Phoca. 



