GENERAL CONSIDERATIONS. 39 



In the general form of the brains that of the sea lion seemed to bear a closer 

 resemblance to that of the bear than either Oallorhinus or Phoca— the latter the least 

 of all. The elongated and narrowed frontal portion of the brain as seen in the bear 

 is represented in Phoca by a foreshortened and broadened region, less marked in 

 Oallorhinus and still less in Zalophus. 



The development of the olfactory lobes is also interesting. They attain their 

 highest growth in the bear, next in Zalophus, then Callorhinus and least, in Phoca, 



The triangular area on each hemicerebrum located between the cruciate and pre- 

 cruciate Assures and the intercerebral cleft, designated by Mivart as the ursine 

 lozenge and believed by him to be of -considerable importance in indicating a phylo- 

 genetic relationship between the Pinnipedia and the ursine group of carnivora, was 

 developed equally well in Zalophus and Oallorhinus. In Phoca it was not observable, 

 although Turner states that in this form it is present but rudimentary and concealed 

 in the mesal fissure of the cerebrum. 



The length of the lateral fissure in Oallorhinus is somewhat unexpected, and in 

 relation resembles the continuous lateral and ectolateral of the bear. In the sea lion 

 and Phoca the lateral is a relatively short fissure. In all but the bear there is an 

 independent ectolateral fissure, but it is not so satisfactorily developed in Phoca. 



The postrhinal fissure shows an interesting variation in the different forms. In 

 Oallorhinus . and Zalophus it has no connection with the rhinal or Sylvian, but is a 

 direct continuation of the subfissure — postica. In Ursus the subfissure may occasion- 

 ally reach to it, but as a rule it is distinct and the postrhinal continues as au elonga- 

 tion of the rhinal. In Phoca the separation of the subfissure and the postrhinal is 

 still more marked, so that the rhinal and postrhinal are practically diiferent parts of 

 one and the same fissure, differentiated from each other by the presence of the 

 Sylvian. 



The presupersylvian fissure is directly continuous with the supersylvian in Ursus; 

 it is likewise continuous in Zalophus and in Oallorhinus except upon the left hemicere- 

 brum of the pup. In Phoca the two fissures are distinctly separated. 



The postsupersylvian is continuous with the supersylvian in Ursus and Zalophus, 

 but separated in Oallorhinus. They are apparently continiions in Phoca, but a dorso- 

 caudal branch and the presence of submerged buttresses at this point of junction 

 would indicate that there was some attempt at separation. 



In the bear there is no elongation of the paracoele to form a postcornu; in the 

 sea lion Murie finds a distinct postcornu present; in Oallorhinus it is quite rudimen- 

 tary; In Phoca Tiedemann represents the paracoele with no appearance whatever of 

 a postcotnu. My own specimen, which, so far as I know, is normal, shows a post- 

 cornu relatively as large or larger than in the primate brain, with a distinct calcar or 

 hippocampus minor in which a portion of the splenial appears as a total fissure. 



With the exception of the bear, concerning which I have no data, and the addi- 

 tional brain from an adult Oallorhinus and Monachus, all of my material was from 

 specimens not more than one year of age. It is believed, judging from a comparison 

 of the brain of the young with that of the adult Oallorhinus as to bulk and complexity 

 of fissuration, that comparatively little or no change occurs, fespecially in the latter 

 respect. 



Mr. Lucas, who has had casts of the cranial cavities prepared from the male and 

 female fur seals, finds but Slight difference in the size of the cavities (see his figures 



