CEEEBEAL CONVOLITTIONS OF THE CAENIVOEA. 



23 



the crucial sulcus, the very wide and voluminous hippocampal 

 gyrus (grooved by secondary sulci xy) rising to the surface behind 

 the crucial sulcus (fig. 9). The fold of cerebral substance thus 

 interposed is far larger than any met vpith in even the Arctoid 

 terrestrial Carnivora. 



Otaria. — The brain of the Sea-Bear * is very instructive, for it 

 supplies what would otherwise be a " missing link " of much im- 

 portance between the brain of the Seals and that of the ordinary 

 land Carnivora. In the first place it is intermediate in general 

 form. It is less rounded than in the Seals, but diff'ers from that 

 of the ordinary Carnivora by being about as broad in front as 

 it is behind. The Sylvian fissure is long (as in the Bears), but 

 more vertical. The three circum- Sylvian gyri are much blended, 

 and the whole cerebrum much convoluted. The parietal and 

 sagittal gyri are very complex and extensively blended by bridging 

 convolutions ; they expand much anteriorly, and surround a very 

 distinct crucial sulcus, which is here placed on the dorsum of the 

 cerebrum (fig. 10). Moreover this crucial sulcus sends forwards 

 converging secondary sulci which produce a very marked and un- 

 mistakable " Ursine lozenge " near the anterior end of the cere- 



Median vertical section of part of brain of Otaria Gilles-pii, 

 half natural size. 

 C. Crucial sulcus. Cm. Calloso-marginal sulcus. Hip. Hippocampal gyrus. 

 Sa. Sagittal gyrus, x ky. Secondary sulci. 



brum. The Ursine lozenge is distinct and large, and the crucial 

 sulcus is very conspicuous. But for the distinctness of this 

 lozenge in Otaria, I should probably have failed to detect the 

 minute and obscure lozenge of Plioca ; and thus the brain of 

 Otaria is truly a link which it would have been unfortunate to 



* This has been described and figured by Dr. Murie, F.L.S. See Trans. 

 Zool. Soc. vol. xiii. pp. 519-527, pi. 78 & pi. 79. fig. 44. 



