28 THE FUR SEALS OF THE PRIBILOF ISLANDS. 



The rhinal fissure is apparently continuous with the Sylvian, but upon raising the 

 overlapping portion of the frontal lobe it is seen to maintain its continuity and to 

 appear again caudal to the Sylvian as a true postrhinal, differentiating a larger 

 pyriform lobe than in the case of Oallorhinus. There is no connection between the 

 postrhinal and the subflss^re in the caudal wall of the Sylvian as in Oallorhinus. 



LATERAL ASPECT. 



The Sylvian fissure pursues a much more obliquely dorso-caudal course than in 

 GallorMnus and presents the same amount of complexity with relation to the surround- 

 ing fissures. In its caudal wall lies a subflssure (postica?) and the intervening Sylvian 

 gyre. Both are relatively better developed than in GallorMnus. The supersylvian 

 has much the same relation to the Sylvian as in GallorMnus. It is not distinctly sep- 

 arated from the postsupersylvian, although the interlocking of some of the subgyral 

 buttresses suggests the possibility of an attempt at separation. On each hemicerebrum 

 there is a continuation of the postsupersylvian dorso-caudad beyond the supersylvian. 



The frontal end of the supersylvian apparently forks, oiie branch bending toward 

 the Sylvian, the other continuing cephalad. The ventral branch has a superficial 

 union with the vertical fissure which has been mistaken for the Sylvian. In my former 

 paper ^ I designated this fissure as the anterior. Krueg also had taken the same view. 



-?--#' 



Pig. 3. PiG. 4. 



Fio. 3. A crons section of a fissure showing the obliquity of its walla. 



Fig. 4. A diagram to show the difference in the course of a fissure at its surface and depth. The heavy lines repre- 

 sent the fisBural walls at the surface. The dotted lines and arrow represent the buttress (b) bounded by the deep course 

 of the fissure. 



From the conditions already described in GallorMnus, it seems to me that this fissure 

 is, after all, a disconnected portion of the supersylvian and that presupersylvian would 

 in some ways be a suitable name for i't. It is submerged in the cephalic wall of the 

 Sylvian for the ventral third of its course. In GallorMnus the ventral two-thirds of 

 the corresponding fissure becomes submerged. 



The lateral fissure, as in the case of GallorMnus, is the longest fissure in the brain. 

 In Plioca, however, it is confined entirely to the dorsal aspect of the cerebrum, and at 

 its caudal end it appears to terminate in a widely diverging fork or perhaps a small 

 transverse fissure, possibly corresponding to the lunate (Wilder) of the cat. Its course 

 is approximately parallel with the intercerebral cleft and is somewhat tortuous. At 

 its cephalic end it appears to communicate with the cephalic branch of the supersyl- 

 vian. This appearance will be discussed more fully under the description of the 

 ansate fissure. 



The eetolateral fissure occupies a relatively higher or more dorsal and caudal 

 position than in GallorMnus. It is of a more secondary character and courses approxi- 

 mately parallel with the postsupersylvian. 



' Loc cit. 



