REPORT ON THE SEALS. 



103 



Table XIII. — Brain of Walrus. 



A cast of the cranial cavity of an adult Walrus gave the following as the three great 

 dimensions of the cerebral hemispheres — length 136 mm., breadth 174 mm., height 

 105 mm. All these dimensions were considerably in excess of the largest of my three 

 brains, so that even when allowance is made for the thickness of the cerebral membranes 

 included in the cast, and for some loss of size from the action of spirit, it is obvious that 

 none of my spirit-preserved specimens represented the full adult magnitude of the organ. 



Viewed from the vertex the cerebrum possessed the form of a broad triangle, the 

 apex of which was forward and truncated, whilst the base was directed backwards ; 

 the sides of the triangle were convex, and the junction of the sides and base was 

 rounded so that the greatest transverse breadth of the cerebrum was distinctly in front 

 of the base. About midway between the base and apex the side of each hemisphere was 

 deeply constricted in the region of the Sylvian fissure (PI. X. fig. 1). This con- 

 striction formed a definite feature in the configuration of the hemisphere ; it curved 

 upwards, inwards, and backwards, and corresponded to a crescent-shaped ridge of bone 

 on the inner aspect of the cranial wall. 



The olfactory bulbs curved upwards in front of the anterior end of the cerebrum, and 

 were almost vertical in direction so as to be adapted to the cribriform plate of the 

 ethmoid. The mesial longitudinal fissure was occupied by the falx cerebri, and the 

 mesial surfaces of the hemispheres were parallel to each other and to the falx for the 

 greater part of their length. Posteriorly they diverged from each other and exposed a 

 portion of the middle lobe of the cerebellum, and the posterior end of the pineal body 

 (fig. 1, P). The angle of the divergence was occupied above by a thick mesial plate of 

 bone continuous with the upper surface of the ossified tentorium and below by the pineal 

 body. The tentorial surface of the lateral lobes of the cerebellum was under cover of 

 the hinder part of the cerebrum, but the occipital surface of the cerebellum was almost 

 vertical, and directed backwards and seen behind the cerebrum. 



The base of the brain was comparatively flattened. The olfactory bulbs in the larger 



