NO. 1325. CEREBRAL FISSURES OF THE WALRUS— FISH. 688 



meters. Only one or two faint traces of minor fissures are evident. 

 It is the simplest gyre of the brain and is contirmous witii the liippo- 

 campal gyre around the splcnium of the callosum. 



I\\'.s/)lenkd^/i.'i-surt'.— This fissure is not well represented on either 

 hemicerebrum of the walrus. On the right heniicerebrum a shallow 

 and short vertical fissure may indicate it. On the left hemicerelirum 

 the only representative of it would be the upper branch of the frontal 

 portion of the splenial. Neither Turner nor Ziehen figures or describes 

 its presence. The fissura sublimica anterior is not shown at all unless, 

 as in Kiikenthars diagram, it is confused with the cruciate. 



P()sts2)lenlaJ JinHure. — In Phoca and Callorhiiuis the tcnitorial portion 

 of the splenial terminates in a bifurcation, the caudal horizontal branch 

 of which is called the post splenial. This is not the case in my speci- 

 men of the walru.s brain. Respecting this region in the walrus. Turner 

 says : 



Behind and below the end of tlie specimen the .splenial fis^snre gave off a postero- 

 horizontal fissnre, which, running horizontally ])ackAvard, extended almost to the 

 posterior border of the hemisphere. * * * The j^ost-splenial fissure of Krueg 

 was situated behind the ascending part of the splenial fissure and ran backward and 

 upward nearly to the postei'ior border of the hemisphere below the postero-horizontal 

 fissure. It was separated from the splenial tissure l)y the splenial convolution, which 

 is consequently bounded in front l)y the splenial and behind by the post-splenial 

 fissure. 



On the left hemicerebrum of my specimen there is a small fissure 

 15 millimeters in length which corresponds in position to the postero- 

 horizontal of Turner. On the right hemicerebrum a mere spur 5 

 millimeters long from the splenial represents it. 



With regard to the post splenial there is found on the right hemi- 

 cerebrum a well-developed vertical fissure branching out of the splenial 

 not far from its tentorial origin. This I regard as the post-splenial 

 fissure, although its direction is vertical anc' not horizontal. On the 

 left hemicerebrimi there is no connection 'letween the splenial and 

 what I regard as the post .splenial. The fi.ssi're is not .so well devel- 

 oped as that described ))v Turner, unless in • y specimen it is an inter- 

 rupted fissure. An unnamed but well-de\'^loped fissure extending 

 dorsally is separated from what I consider tht^'bost splenial by a cortical 

 isthnms of only 4 millimeters' width. Thtf' "appearances suggest an 

 interrupted fissure. Turner docs not de.-.-rr.c any coimection between 

 the po.st-.splenial and splenial fissures, bnt calls the intervening space 

 the .splenial convolution (gyre). 



Marginal f.s.siire. — In Zalophus, Phc- \ and Oalloi'hinus this is a 

 well-de^•eloped fissure hnng between, a: approximately j)arall('l with, 

 the .splenial and medilateral fi.ssures. ' ^eems to con-espond in man}^ 

 cases with the suprasplenial fissure of i ^ueg, and in some .special cases 

 with the combined post and supra s'->lenial of the .same author. In 

 the walrus the marginal is not especial I3' well developed. On both 



