THE CEREBRAL FISSURES OF THE ATLANTIC WALRUS. 



By PiERKE A. Fish, 



Of Cornell Univermty, Ithaca, Neir York. 



Through the courtesy of the officials of the U. S. National Museum 

 there were sent to me, for examination and description, two walrus 

 brains obtained for that institution by R. Stein at North Greenland, 

 August 10, 1901. The specimens had been preserved in a fluid of 

 which formaldehyde was apparently a constituent. In both brains the 

 cerel)ellum had been removed b}' a sectit.n through the brain stem at 

 the level of the junction of the optic thalami with the mesencephal, so 

 that in the process of removal the epiphysis (pineal body) remained 

 attached to the cerebellar portion; the two hemicerebrums were then 

 divided b^' a median section. 



The two brains difl'ered quite markedly in size, the one being but 

 slightly more than half as large as the other. The smaller of the two 

 brains had sufiered quite material mutilation during its removal from 

 the cranium, a considerable portion of the brain substance having ))een 

 lost fi'om the right hemicere1n-um. Li the process of hardening all of 

 the hemicerebrums had undergone considerable distortion. The mesal 

 surface in each case, instead of being relativeh' flat, was very dis- 

 tinctly convex in its cephalo-caudal direction, and on this account 

 the gyres (convolutions) and Assures of the lateral aspect were closely 

 crowded together, rendering the study of these parts more diflicult. 

 On this account, also, it was decided not to photograph the brains, as 

 the relationship of the parts would l)e misleading and tend to cause 

 error and confusion to the observer. The tigures which illustrate 

 this article were sketched free-hand, the parts at the same time being 

 manipulated so as to bring them as nearly as possible to their normal 

 relations. By carefully verifying each part on the l)rain itself as the 

 drawing progressed, it is believed the tigures may be accepted as 

 representing with approximate accuracy the normal i-elatiojiship of 

 the more important parts. 



Weight. — Turner" gives tli(> weights of tlii-ce walrus brains •"after 



« Challenger Reports, Zoology, XXVI, 1888, pp. 89-134. 



Proceedings U. S. National Museum, Vol. XXVI— No. 1325. 



675 



