846 PROFESSOR DAVID HEPBURN ON 
The rhomboid or 4th 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 vag formed quite recognisable elevations. The 
area acustice was likewise a well-marked elevation on the floor, but its surface was 
smoother than in man because of the absence of visible strize on its free surface. The 
emunentia 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 Reil 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 calearine 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. 
