32 THE FUR SEALS OF THE PRIBILOF ISLANDS. 



the fissures were not sounded as thoroughly as in the other spe(!imens. The cerebrum 

 of this specimen does not show the same degree of complexity relative to the fissura- 

 tion as indicated byMurie"^ in Otaria juhata. A direct comparison of the flssureSj 

 however, is not easy, as the latter author attempts to homologise them with those of 

 the human cerebrum. 



The olfactory apparatus is well developed. Not as largely as in the bear, however, 

 but greater than in either of the seals. The rhinal fissure, as in the other forms, is 

 well marked, and passes caudad into the mouth of the Sylvian fissure. The i)ost- 

 rhinal is formed from the subfissnre (postica?) and has no connection whatever with 

 either the rhinal or Sylvian. 



LATERAL ASPECT. 



The Sylvian is prominent and occupies its usual position. In its caudal wall is a 

 subfissnre (postica?) and subgyi^e, which, as in CallorJiinus, is continuous on the 

 ventral aspect with the pyriform or temporal lobe. 



The supersylvian, with its cephalic and caudal portions, the pre- and postsuper- 

 sylvian, is more nearly in accord with the conditions found in the bear than in either 

 of the seals. It repr.esents an intermediate condition between the two. The presuper- 

 sylviau li€s very close to the Sylvian, but does not actually enter it, as in the seals. 

 Its average distance from it is about 4 millimeters, while the distance frOm the Sylvian 

 to the postsupersylvian is four times as great, or 16 millimeters. There is no sign of 

 disconnection laetweeu either the supersylvian and the postsupersylvian, or the super- 

 sylvian and the presupersylvian. The supersylviau forks or sends out a branch 

 cephalad connecting with the ansate fissure exactly as in Phoca. 



The lateral fissure is, relatively to the length of the cerebrum, shorter than in any 

 of the other forms. Its cephalic end and its relation to the ansate is again exactly the 

 same as in Phoca. On the left hemicerebrum the lateral is disconnected at a little more 

 than half of its length by a narrow isthmus. 



The coronal fissure corresponds with that of Phoca, connecting, superficially at 

 least, with the ansate, and thus, indirectly, with the cephalic branch of the supersylviau 

 and the lateral. 



The ansate fissure, as has already been intimated, like that of Phoca, is irregular 

 in its form and connects with the fissures above mentioned. 



The ectolateral fissure is quite well down toward the ventral portion of the cere- 

 brum and, as in Callorhinus, appears upon the ventral aspect. 



The medilaterai fissure is scarcely perceptible on the lateral aspect; it lies exactly 

 along the caudal margin of the hemicerebrum, as in Gallorhinus, and is better seen in 

 a mesal view. 



The cruciate accords, in position and relation, more closely with the conditions 

 found in the bear and Callorhinus; but while it reaches to the mesal surface of the 

 hemicerebrum it does not cut it as far as in the bear and Phoca. 



Theprecruciate and the postcruciate fissures fife likewise present and have exactly 

 the same relations as in the bear and Gallorhinus. 



MESAL ASPECT. 



The callosal fissure is well developed. On the right hemicerebrum it does not 

 continue around the genu, as in the left. 



' 1874, Transactions of the Zoological Society of London. 



