REPORT ON THE SEALS. 93 



of the olfactory bulbs appeared for a short distance in front of the anterior end of the 

 cerebrum. The two hemispheres were parallel, and formed the sides of the mesial 

 longitudinal fissure, but at the posterior end they diverged slightly from each other 

 so as to expose a small portion of the middle lobe of the cerebellum. The space between 

 the diverging hemispheres was occupied by a mesial plate of bone continuous with the 

 upper surface of the ossified tentorium. 



The cerebellum projected behind the base of the hemispheres, and the surface of the 

 cerebellum which was exposed was the posterior or occipital, the general direction of 

 which curved from above downwards and backwards. The anterior or tentorial surface 

 again sloped downwards and forwards, and was completely concealed by the cerebral 

 hemispheres, except the small portion of the middle lobe above referred to. In my paper ' 

 On the Anatomical relations of the surfaces of the Tentorium to the Cerebrum and Cere- 

 bellum, I pointed out that in the brains of the Carnivora the surface of the cerebellum 

 which is exposed behind the cerebrum is the occipital, or that which corresponds to the 

 inferior surface of the human cerebellum, and not the anterior or tentorial surface, which 

 is the superior surface of human anatomy. At the time when that paper was published I 

 had not seen the brain of the Seal in situ, but in the summer of the same year I had the 

 opportunity of seeing the brains both of a young Phoca grcenlandica and a Halichcerus 

 grypus in the crauial cavity. In the Greenland Seal the cerebellum was below the 

 hinder part of the cerebrum, and its occipital surface was almost vertical, though with a 

 slightly forward direction. In Halichcerus grypus the occipital surface of the cere- 

 bellum was posterior and almost vertical, the vermiform process being the most projecting 

 part ; the cerebellum was below the cerebrum, but, owing to a slight divergence of the 

 cerebral hemispheres posteriorly, a part of the vermiform process could be seen between 

 them when the brain was looked at from above. In the Elephant Seal the cerebellum 

 was apparently exposed to a greater extent than in the Greenland and Grey Seals. 



The base of the brain was comparatively flattened, owing to the shallowness of the 

 middle cranial fossae. The olfactory bulbs were almost vertical in direction, in conformity 

 with that of the cribriform plate of the ethmoid bone. The olfactory peduncle was 

 21 mm. long. It was remarkably slender, more so even than in the human brain, and 

 was almost entirely concealed in the olfactory sulcus. It terminated posteriorly in a 

 slight elevation, situated in front of the inner end of the Sylvian fossa, and of the locus 

 perforatus anticus. This elevation, the trigonum or tuber olfactorium, was 16 mm. long 

 and 5 mm. broad, and was directed backwards and outwards into the Sylvian fissure. It 

 is possible that another root had passed inwards to the great longitudinal fissure, but it 

 was not clearly marked, for the surface of the brain was somewhat abraded at this spot. 

 The optic nerves, commissure, and tracts were all very distinct, and the last named 

 curved backwards on the outer aspect of the crura cerebri. The third nerves arose from 



1 Proc. Roy. Soc. Edin., March 3, 1862, vol. iv. p. 549. 



