BRAIN OF CALLORHINUS. 33 



The splenial fiasure does not extend as far cepbalad as in Gallorhinus, nor as far 

 dorsad as in Phoca. It is situated more closely to the splenial half of the callosum than 

 in either of the preceding or in the bear. A branch is given oft' in the region of the 

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

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



Tlie prespleuial is not represented as a distinct fissure on the left hemicerebrum, 

 the ouly possible suggestion of it being a forking at the cephalic eud-of the splenial. 

 On the right liemicerebrum a small but distinct tissure lying cephalad of the splenial 

 may represent the presplenial. 



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

 surface, as in Callorhinus. In Phoca, althougli relatively long, it does not reacli the 

 dorsal margin at all. In the bear the marginal Assure 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. 



FISSUKAL INTERPRETATIONS OF 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 the 

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

 tion as the anterior and x)osterior branches of the Sylvian. The two fissures morpho 

 logically are entirely distinct. In Hyrax Krueg does not represent any indication of 

 a Sylvian fissure whatever. 



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

 have confused this fissure with the lateral in Phoca. 



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

 commonly known as the x^ostsylvian 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 iiresylvian 

 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 Odolxcnus (walrus) he figures as the presylvian an apparent 

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

 a third arched fissure, designated by him as the medilateral. 



The superorbital fissure in caruivora 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 the presplenial, or anterior subliuiica of Kiikenthal. 

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

 cephalic end. Other writers place it as 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 (PARACOELE). 



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

 the lateral ventricle is revealed. In the bear the cavity bends cephalo-ventrad to 

 5974— PT 3 3 



