36 THE FUR SEALS OF THE PRIBILOF ISLANDS. 



corresponding to that of Mo7iachus, but it does not extend deeply euougli to connect 

 with tbe postica. 



The postrhinal api)ears as tbe merest trace of a fissure, and Las a very superficial 

 connection with the postica. 



Tbe Siilvia7i fissure. It is in tbe Sylvian region tbat we get numerous clews to 

 tbe intermediate position of Monachus. In tbe brain of tbe female, tbe Sylvian lias 

 practically tbe same direction as in Callorhinus. In tbe male, tbe true Sylvian really 

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

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

 accounted for by tbe nearly complete disai)pearance of tbe postica. 



The presupersylvian resembles tbe corresponding fissure in J'hoca regarding its 

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

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

 supersylvian. 



Tbe Hupersylvian fissure resembles that of Phoca in extending a l)ran(!h of good 

 size to connect with tbe an sate. 



Postsupersylvian. — In tbe two hemicerebrnms of tbe male there was a connection 

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

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



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

 It forms a good intermediate stage between Callorhinus 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 bemicerebrums of both brains the cruciate is apparently continuous 

 with tbe spleuial. lJi)on the right hemicerebrnms there is no such connection. 



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

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

 surface, and its lateral end makes a very decided curve toward the coronal fissure. 

 There is almost a superficial connection between tbe cruciate and precru(!iate. The 

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

 of their almost complete mergence into ejich other. 



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

 guishable, smaller than in any of tbe 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 tbe least satisfactorily represented 

 than in any of tbe other forms. In tbe two hemicerebrnms it does not seem to be 

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

 i:ig it. In the right bemicerebrums the fissure is distinctly present, but is very small. 



Tbe Spleniat accords more closely with Phoca in its position, reaching tbe mid- 

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

 branch coiresponding to the postsplenial as in tbe other brains. 



Tbe Presplenial is well represented in tbe two right hemicerebrnms, but in tbe 

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

 submerged buttresses at tbe 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 or interrupted fissures take its place. 



