. . BRAIN OF CALLOEHINUS. 33 



The splenial fissure does not extend as far cephalad as in Gallorkinus,nor as far 

 dorsad as in Fhoca. It is situated more closely to the splenial half of the callosura than 

 in either of the preceding or in the bear, A branch is given off in the region of the 

 splenium proper which seems comparable to the postsplenial in the seals. A slight 

 spur in this region in the bear may indicate an analogy. 



The presplenial is not represented as a distinct fissure on the left hemicerebrura, 

 the only possible suggestion of it being a forking at the cephalic end of the splenial. 

 On the right hemicerebrum a small but distinct lissure lying cephalad of the splenial 

 may represent the presplenial. 



The marginal fissure is well represented, and on both hemicerebrums cuts the dorsal 

 surface, as in Gallorhinus. In Phoca, although relatively long, it does not reach the 

 dorsal margin at all. In the bear the marginal fissure is not represented. 



The genual and rostral fissures are but slightly developed in this specimen and 

 bear the same relations as in other forms. 



The cruciate fissure shows slightly on the mesal aspect, and in its relations to the 

 other parts resembles that of the bear more than any of the others. 



PISSUBAL INTERPRETATIONS OP OTHER WRITERS. 



The Sylvian fissure, in Phoca, at least, has been located as a vertical fissure (pre- 

 supersylvian) which has, for a portion, only, of its length, been submerged in tlie 

 cephalic wall of the true Sylvian, Numerous writers have also described this condi- 

 tion as the anterior and posterior branches of the Sylvian. The two fissures morpho 

 logically are entirely distinct. In Ryrax Kraeg does not represent any indication of 

 a Sylvian fissure whateyei'. 



The supersylvian is very commonly called the suprasylvian. Leuret and Gratiolet 

 have confused this fissure with the lateral in Plwca. 



Following Krueg, the fissure which is designated as the postsupersylvian is 

 commonly known as the postsylvian of Owen. What I have designated as the pre- 

 supersylvian, and which is only exceptionally independent, is usually described as 

 the anterior or frontal portion of the supersylvian. 



A fissure corresponding to the coronal is represented by Krueg as the presylvian 

 in Phoca. Kiikenthal makes a similar representation. Turner, in Macrorhinus, 

 represents a corresponding. fissure as the presylvian and a branch connecting with it 

 as the coronal. In Odobanus (walrus) he figures as the presylvian an apparent 

 continuation of the lateral, and represents as the coronal an apparent continuation of 

 a third archedtfissure, designated by him as the medilateral. 



The superorbital fissure in carnivora generally is designated as the presylvian by 

 many writers. 



The cruciate fissure is shown by Krueg, in Phoca, as existing only on the mesal 

 aspect, occupying the position of thie presplenial, or anterior sublimica of Kiikenthal. 

 Leuret and Gratiolet represent the fissure as seen on the ventral aspect at the 

 cephalic end. Other writers place it 3,8 usually seen in carnivora at the cephalic end 

 of the dorsal aspect, where it may or may not reach the mesal surface, 



THE LATERAL VENTRICLE (PARACOBLE). 

 On removing the dorsal portion of the hemicerebrum just dorsal to the callosum 

 the lateral ventricle is revealed. In the bear the cavity bends cephaloventrad to 

 5974— PT 3 3 



