S6 Journal of Comparative Neurology. 



the Sylvian fissure and the intervening portion of the Sylvian 

 gyre, besides being narrower than in the bear, has also sunk 

 slighly lower than the adjacent surface as if prophesying the 

 conditions found in the seals. 



In the seals there appears to be some evidence, if the inter- 

 pretation as to the frontal portion of the supersylvian fissure be 

 correct, that after breaking up into branches with perhaps some 

 disconnection of its parts, it shows a tendency to follow the ex- 

 ample of the anterior-postica fissure, because in Phoca, at least, 

 the supersylvian bifurcates a little beyond the free end of the 

 Sylvian, one branch forming a well defined arch around it, the 

 other branch passing on in the frontal region. The branch, 

 however, which forms the arch is not a long one but it extends 

 to and superficially connects with a vertical fissure which for half 

 its distance is submerged in the frontal wall of the Sylvian, and 

 crops out again on the ventral aspect of the brain. This con- 

 dition holds for both hemicerebrums of Phoca. CallorJmius 

 throws a little light on this matter. In the right hemicerebrum 

 the supersylvian is clearly continuous with the vertical fissure 

 submerged in the frontal wall of the Sylvian but gives off a very 

 short frontal branch. Superficially it is continuous with the post- 

 supersylvian but a shallow at this point indicates a partial sep- 

 aration. The direct continuity in the depth of the supersylvian 

 with the vertical fissure would seem to point to the fact that the 

 latter, after all, was nothing more than the frontal portion of 

 the supersylvian, namely the presupersylvian. 



In the left hemicerebrum the parts are a little more com- 

 plicated. The postsupersylvian is entirely separated, the super- 

 sylvian is entirely distinct from the frontal portion and is quite 

 irregular and branching in its course, but mainly vertical in its 

 direction. 



Thus, taking the canine brain as exemplifying a simple fis- 

 sural pattern and passing through the Felidae and Ursidae and 

 sea lion to the seals where the fissures are more numerous and 

 complicated by the presence of branches of considerable size, 

 and more or less disconnection of some of the principal fissures, 

 we may arrive at some understanding of the relationship and 



