28 THE FUR SEALS OF THE PRIBILOF ISLANDS. 



The rhinal fissure is apparently coutiuuous 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 

 pyriforin lobe than in the case of Cnllorhinvs. There is no connection between the 

 postrhinal and the subfissure in the caudal wall of the Sylvian as in Callorhinus. 



LATERAL ASPECT. 



The Sylvian fistanre pursues a rauch more obliquely dorso-caudal course than in 

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

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

 gyre. Both are relatively better developed than in Callorhinus. The supersylviau 

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

 arated from the postsupersylvian, althongh 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 dorsocaudad beyond the supersylviau. 



The frontal end of the supersylviau apparently forks, one 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. 



Fio. 3. 



Fio. 3. A cross section of a fissnre showiDg the obliqnitj' of its walls. 



Flo. 4. A (lia(;ram to show tlio (lifFerence in the courso of a tissure at its surface and depth. The heavy linos repre- 

 sent the tissiiral walls at the Burface. Tlie dotted lines and arrow represent the hnttress (b) hounded hy the deep course 

 of the fissure. 



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

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

 in some ways be a suitable name for it. It is submerged in the cephalic wall of the 

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

 the corresponding lissure becomes submerged. 



The lateral Jissiire, us in the case of Callorhinus, is the longest fissure in the brain. 

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

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

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

 is api)ioximately ])arallel with the iutercerebral cleft and is somewhat tortuous. At 

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

 viau. This ai)pearance will be discussed more fully under the description of the 

 an sate fissure. 



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

 position than in Callorhinus. It is of a more secondary charatiter and courses approxi- 

 mately parallel with the postsupersylvian. 



' Loc cit. 



