Fish, Brain of the Fur ■ Seal. 63 



in the Caiiidac the super-sylvian forms a complete arch, the cau- 

 dal portion being known as the posterior supersylvian (Kriieg), 

 or postsylvian (Owen). The frontal portion of this arch varies 

 in its distance from the Sylvian. Occasionally the frontal and 

 caudal portions are about equally distant, but when there is any 

 difference in this distance, it appears that the frontal portion ap- 

 proaches more closely to the Sylvian than does the caudal. In 

 Ursus aictos, or the brown bear, Krueg figures the frontal por- 

 tion of the supersylvian as approximating very closely to the 

 Sylvian. The condition in CallorJiinus might be considered as 

 a stage just beyond this. In the brown bear the frontal portion 

 of the supersylvian is still visible upon the lateral surface close to 

 the Sylvian. In the case of the seal it has passed over the 

 brink, so to speak, and is no longer visible its entire length on 

 the lateral surface. The following diagrams will illustrate the 

 conditions more clearly. 



Fig. ]. Fig. 2. 



Fif;s. I and 2. A diagrammatic representation of the relation of the Sylvian 

 and supersylvian fissures in the bear and seal, as if seen in section, prss, pre- 

 supersylvian. pss, postsupersylvian. Syl, Sylvian fissure. 



At the bottom of the Sylvian fissure lies the insula, pre- 

 senting but a slight degree of development. There is a sugges- 

 tion of a circuminsular fissure but in other respects the surface 

 is entirely smooth. In the caudal wall of the Sylvian is a well 

 marked subfissure. It separates a portion of the concealed cor- 

 tex, forming a subgyre, which from its size and position might 

 be easily mistaken for the insula. The appearances would sug- 

 gest that the subfissure is the postica and the subgyre a rem- 

 nant of the Sylvian gyre. 



The supersylvian fissure shows some variation on the two 

 sides. It presents the usual arrangement on the right hemice- 

 brum, forming, superficially' at least, a complete arch around 



