36 THE FUR SEALS OP THE PRIBILOF ISLANDS. 



corresponding to that of Monachus, but it does not extend deeply enough to connect 

 with the postlca. 



The postrhinal appears as the merest trace of a fissure, and has a very superficial 

 connection with the postica. 



The Sylvian fissure. It is in the Sylvian region that we get numerous clews to 

 the intermediate position of Monachus. In the brain of the female, the Sylvian has 

 practically the same direction as in Gallorhinus. In the male, the true Sylvian really 

 branches cephalad, although there is a superficial extension in the usual dorso-caudal 

 direction. Apparently some unusual conditions exist here, which may perhaps be 

 accounted for by the nearly complete disappearance of the postica. 



The presupersylvian resembles the corresponding fissure in Phoca regarding its 

 extreme vertical position and apparent union with the Sylvian for only the ventral 

 third of its course. It differs from Phoca in not being disconnected from the 

 supersylvian. 



The supersylvian fissure resembles that of Phoca in extending a branch of good 

 size to connect with the ausate. 



Postsupersylvian. — In the two hemicerebrums of the male there was a connection 

 between the supersylvian and the postsupersylvian, much as in Phoca. In the 

 hemicerebrums of the female there was an entire disconnection of these fissures. 



The cruciate fissure more than in any of the others resembled that of the Phoca. 

 It forms a good intermediate stage between Gallorhinus and Phoca. As with Phoca 

 the fissure is represented on the mesal surface as much, if not more than, upon the 

 dorsal. In the left hemicerebrums of both brains the cruciate is apparently continuous 

 with the splenial. Upon the right hemicerebrums there is no such connection. 



Precruciate. — In all four hemicerebrums the precruciate extends over upon the 

 mesal surface for some little distance. It is more largely represented upon the dorsal 

 s'urface, and its lateral end makes a very decided curve toward the coronal fissure. 

 There is almost a superficial connection between the cruciate and precruciate. The 

 conditions in Phoca indicate that such a connection has occurred even to the extent 

 of their almost complete mergence into each other. 



" Ursine lozenge." — This area is, with the exception of Phoca, where it is undistin- 

 guishable, smaller than in any of the other forms. It is nothing more than a narrow 

 gyre, situated at a slightly lower level than the adjacent gyres, suggesting a probable 

 preparation of its loss of identity in Phoca. 



Postcruciate. — In Monachus this fissure was the least satisfactorily represented 

 than in any of the other forms. In the two hemicerebrums it does not seem to be 

 represented at all, unless we interpret a slight branch from the cruciate as represent- 

 ir)g it. In the right hemicerebrums the fissure is distinctly present, but is very small. 



The Splenial accords more closely with Phoca in its position, reaching the mid- 

 dorsal region instead of extending farther cephalad, as in Gallorhinus. It sends off a 

 branch corresponding to the postspleuial as in the other brains. 



The Presplenial is well represented in the two right hemicerebrums, but in the 

 two left it appears to connect the true splenial with the cruciate. Tbe interlocking of 

 submerged buttresses at the proper points indicates a superBcial connection merely. 



The Marginal fissure is more poorly developed than in any of the other forms 

 except the bear. A series of short or interrupted fissures take its place. 



