64 Journal of Comparative Neurology. 



the Sylvian. The presence of a shallow and a slight bifurcation 

 near the level of the free end of the Sylvian indicates the sep- 

 aration of a postsupersylvian fissure, postsylvian of other 

 writers. Plate I, Fig. 4. The supersylvian curves around the 

 free end of the Sylvian at a rather sharp angle and soon appar- 

 ently enters the Sylvian, but in reality is submerged in its 

 cephalic wall. A very short cephalic branch is given off toward 

 the ansate fissure before the supersylvian enters the Sylvian. 

 On the left hemicerebrum there are three distinct portions ; the 

 postsupersylvian has a slightly more oblique dorso-caudal course, 

 the supersylvian proper is quite branching and more inclined to 

 a vertical than a horizontal course. One of its branches appears 

 to enter the Sylvian from behind but a shallow shuts off any deep 

 connection. The frontal portion appears as a surface fissure for 

 only one third of its course, then, as on the other side, it becomes 

 submerged in the Sylvian. As this portion bears much the 

 same relation to the supersylvian as the postsupersylvian 

 whether they be disconnected or not, the frontal portion will be 

 designated as the presupersylvian fissure. In the second speci- 

 men of the brain of an adult Callorhinus, kindly loaned to me 

 by Mr. True, the executive curator of the U. S. National Mu- 

 seum, both hemicerebrums showed a distinct separation of the 

 postsupersylvian, more pronounced than on the right hemice- 

 rebrum of the pup ; but there was no separation nor distinct ap- 

 pearance of a shallow indicating an independent presupersylvian 

 as in the left hemicerebrum of the pup. In the adult, as in the 

 pup, each supersylvian gave off a short cephalic branch before 

 entering the Sylvian. 



The Lateral fissure, on account of the breadth of the brain, 

 does not show in its entirety upon the lateral aspect. It is 

 twelve centimeters long, by far the longest fissure, and is seen 

 for a short portion of its course upon the ventral aspect extend- 

 ing, on the left hemicerebrum, to within five millimeters of the 

 ventral portion of the postsupersylvian. It lies in this region 

 just in advance of the margin of the cleft between the cerebrum 

 and the cerebellum. It then arches caudo-dorsally approxi- 

 mately parallel with the hemicercbral margin but receding from 



