678 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



and disconnected postsupersylvian fissure. In the cat there is usually 

 a disconnection between the supcrsylvian and postsupersylvian, and 

 occasionally this disconnection is seen in ('allorhinus and Monachus. 

 On the other hand, the vertical fissure is much shallower than the 

 supersylvian, and the latter is contiinious with a deep and well- 

 developed fissure apparent^ correspondin*^- with the postsupersylvian 

 of the sea lion, Phoca, bear, and dog. 



The matter is further complicated by the fact that if this be regarded 

 as the postsupersylvian, it is longer than usual, since it passes down 

 from the lateral surface and appears upon the ventral aspect, and lies, 

 in part, in the situation generally occupied b}^ the ectolateral fissure. 

 The ectolateral generall}^ occupies a jjosition Ix'tween the postsuper- 

 sylvian and lateral fissures; sometimes it comiects with the lateral, ))ut 

 rarely with the pontsupersylvian, although such a connection was once 

 observed by me on the hemicerebrum of a young fur seal. The exam- 

 ination of a luunber of brains shows that the ectolateral is a more 

 varia])le and inconstant fissure than the postsupersylvian, and in the 

 present specimen of the walrus brain it seems safer to infer that the 

 postsupersylvian and ectolateral have run together to form a king 

 and continuous fissure and that the vertical iissure above mentioned is 

 an unusually well-developed minor fissure. In the sea lion, where this 

 region is so similar to that of the Avalrus, the postsupersylvian is a 

 shorter fissure and is entirely disconnected from the ectolateral. 



The si/lv/'an gyre is that arch-like portion of the cortex around the 

 sylvian fissure included within the boundary line formed by the super- 

 sylvian and pre- and post-supersylvian fissures. The cephalic limb of 

 the gyre is narrow and completely submerged in the ventral third of 

 the sylvian fissure. The caudal limb has a much greater area, being 

 easily four times as wide as the cephalic. A few minor fissures branch 

 out from the sylvian into this frontal limb. The caudal limb has a 

 greater number of these fissures, and one in particular is developed to 

 such an extent as to suggest the possibility of its representing the 

 postsupersylvian. 



Lateral .finmre. — This fissure is unequally developed on the two 

 hemicerebrums. The well-defined arch which it forms in some car- 

 nivorous and seal brains is not well represented in the walrus. On 

 the left hemicerebrum it is apparently an interrupted fissure; a 7V/ de 

 passage or fold of cortex separates it a little in front of the level of 

 the sylvian. From this point on it arches fprward and downward. 

 Caudallv it does not extend bej^ondthe level of the caudal end of the 

 supersylvian. On the right hemicerebrum, instead of arching in a 

 caudal direction it extends toward and nearly reaches the mesal surface. 

 A short fissure having the direction tiie lateral should take is separated 

 from the lateral proper b}- a narrow pll de jxixxagc The lateral 

 fissure of the sea lion accords quite closely with that of the walrus, in 



