134 PROFESSOR DAVID HEPBURN ON 



The rhomboid or ktli ventricle was distinctly lozenge-shaped, but neither in regard 

 to its size nor in regard to the detailed modelling of its floor was it so well marked as in 

 man. The floor presented a median furrow, as well as an inferior and a superior fovea 

 in relation to each quarter of the lozenge. Associated with the fovea inferior, the 

 trigonum hypoglossi and the trigonum vagi formed quite recognisable elevations. The 

 area acusticse was likewise a well-marked elevation on the floor, but its surface was 

 smoother than in man because of the absence of visible strise on its free surface. The 

 eminentia teres was placed to the mesial side of the superior fovea, but it was prolonged 

 upwards as well as downwards by a longitudinal ridge which ran upwards along the 

 floor of the aqueduct of Sylvius in the one direction, and downwards to join the trigonum 

 hypoglossi in the other. 



The obex was a distinct object in the roof of the ventricle in relation to its inferior 

 angle, and the ligula could be seen extending from it on each side. 



SUMMARY. 



In making a general summary of the naked-eye anatomy of the brain of the 

 Weddell seal, the features which have impressed me most and seem most deserving 

 of special reference are the following : 



1. Its angular appearances in association with its large size, suggesting that the 

 general fish-like outline of the entire animal has to a certain extent influenced the 

 shape of its skull, and thereby the shape of the brain within the cranium. 



2. The size and elaborate ramification of the cerebral convolutions, together with 

 the considerable amount of asymmetry in the details of the arrangement of the 

 convolutions of the one hemisphere as compared with the other. 



3. The width of the interval between the two hemispheres posterior to the hinder 

 end of the corpus callosum. 



4. The marked departure from the arrangement of the cerebral convolutions in 

 such a typical carnivore as the dog. 



5. The presence of those convolutions belonging to the island of Eeil upon the 

 same superficial plane as that of the surrounding convolutions which form the 

 opercula. 



6. The definite and complete character of the limbic lobe. 



7. The position of the calcarine fissure, and thereby of the visual area upon the 

 inferior aspect of the occipital end of the hemisphere. 



8. The large size of the fornix, and particularly of its posterior pillars, in association 

 with a well-marked hippocampus major, of which the greater part is composed of 

 fornix fibres and only a small part of grey substance. 



9. The long stalk and the large size of the pineal body and its position upon the 

 vermis of the cerebellum, in the open interval between the cerebral hemispheres. 



10. The well-developed but, on the whole, simpler characters of the basal structures 

 as compared with the elaboration of the pallium. 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 846.) 



