NERVOUS SYSTEM. VERTEBRATA. 293 



The calcarine is separated from the intercalary merely 

 by a submerged gyms. There is a shallow marginal 

 sulcus, in addition to the compensatory ansate. 



There are rostral and genual sulci. The latter is sepa- 

 rated from the sulcus which bisects the Ursine lozenge, 

 merely by a submerged gyrus. 



Ziehen, Anat. Anzeiger, Bd. v. 1890, p. 692. 



D. 374. A cast of the cranial cavity of a Walrus (Odobcenus 

 [Triclieclius] rosmarus). [In duplicate.] 



Eamily PHOCIDJE. 



D. 375. The brain of a foetal Common Seal (Phoca vitulina). 



The shape of the hemispheres of the Common Seal differs 

 most markedly from that of Otaria and Odobcenus. 



[This account is based not on this specimen but on a 

 damaged specimen in the Stores.] 



There is no great indentation of the lateral contour in 

 the Sylvian region as in Otaria and Odobcenus. The 

 hemispheres present an elliptical appearance when viewed 

 from above and an ovoid form in profile. The anterior 

 pole is blunt and rounded, the posterior pole is prolonged 

 backward to cover the cerebellum and carries with it a 

 diverticulum (posterior cornu) of the lateral ventricle. 



The upper extremity of the pseudosylvian sulcus appears 

 to bifurcate. The anterior branch is formed by the anterior 

 vertical portion of the suprasylvian sulcus emerging from 

 the Sylvian fissure, in the anterior lip of which it is placed 

 as in the Walrus. This overlaps without joining the 

 horizontal part of the suprasylvian. 



The posterior limb of the bifurcation probably represents 

 the upper part of the anterior ectosylvian sulcus or the 

 "Ursine Sylvian fissure." 



As a result of the backward growth of the hemisphere, 

 the postsylvian sulcus is very oblique. It is joined to the 

 horizontal arc of the suprasylvian, and is also prolonged 

 far beyond the junction to reach the apex of the occipital 

 pole. 



