30 THE FUR SEALS OF THE PRIBILOF ISLANDS. 



Tlie marginal or supersplenial is well shown in Phoca as in Callorhinus, but lies 

 nearer to the dorso-caudal margin, approximately parallel with the splenial. In the 

 intervening gyre there are a few secondary fissures. 



On the meso-ventral surface a fissure corresponding to the collateral is also 

 present, but, unlike Callorhinus, it has connection with the postrhinal. Between the 

 collateral and the postsplenial there is another well-marked but unnamed' fissure which 

 is parallel to the former. It corresponds, perhaps, to the fissure in Gallorhinus which 

 I have spoken of tentatively in connection with the occipital. 



The genualis and rostralis are represented, but the latter differs from that in 

 Gallorhinus in being much less developed and occupying a more ventral position at a 

 more or less acute angle to the genualis. 



URSUS AMERICANUS. 



This brain, while fairly well preserved, had been considerably mutilated in removal, 

 so that for purposes of illustration and reference, a specimen from Ursus thibetianus, 

 kindly loaned by Prof. B. G. Wilder, was utilized ; so that while the figures of the 

 lateral and mesal aspects are from the latter specimen, the description is based almost 

 entirely upon the former. The general arrangement of the fissures is similar, and the 

 minor details need not cause misapprehension. The fissural plan of the brain is much 

 like that of the canine, minus the first circumsylvian arch. 



The olfactory bulbs and crura are far superior in size to those of either of the 

 seals. The olfactory fissure is likewise well marked. 



The rhinal fissure 'passes into the Sylvian and continues, after forming an angle 

 delimiting a well-developed pyriform lobe, as the postrhinal, and ending freely. 



The subfissure (postica?) in the caudal wall of the Sylvian extends to and on one 

 side actually appeared to communicate with the postrhinal. 



LATERAL ASPECT. 



The Sylvian is directed in the usual dorso-caudal direction at the bottom of which 

 is a small and simple area representing the insula. There is no appearance of a 

 transinsular fissure, although th'e presence of a subgyre and. subfissure (postica?) in 

 the caudal wall of the Sylvian might superficially indicate it. 



The supersylvian fissure forms a complete arch around the Sylvian. There is no 

 indication of a separation of a post supersylvian except near the free end of the Syl- 

 vian, where a branch from the supersylvian extends into the adjacent gyre. 



The lateral fissure forms a curve approximately parallel with the supersylvian. 

 As compared with Phoca and Gallorhinus it is much shorter. If the concejition of 

 the ectolateral is correct, the latter is continuous caudally with the lateral, a slight 

 spur indicating the place of probable separation. The ectolateral extends parallel 

 with the postsupersylvian, but its ventral end does not reach so far in Vrsus ameri- 

 eanus, while in the Thibet bear the reverse is the case. 



The ansate fissure is a cephalo-ventral continuation of the lateral, a small spur 

 of the latter indicating a point of separation. The ansate describes a curve, the con- 

 vexity pointing toward the Sylvian. 



The coronal fissure continues from the ansate and ends freely near the superor- 

 bital. The convexity of its curve like that of the ansate points toward the Sylvian. 

 The point of its separation from the ansate is indicated by a spur more marked than 

 that between the ansate and the lateral. 



