THE ANATOMY OF THE WEDDELL SEAL. 839 
the cornu was reduced to a narrow band in close relation to the concave margin of the 
hippocampus. Consequently, in the brain of this seal the hippocampus major could not 
be described as the reverse or ventricular surface of the sulcus hippocampi. 
Again, the pes hippocampi terminated as a rounded end, only slightly wider than 
the general body of the object and not expanded or notched as in man. 
The fimbria hippocampi occupied the concavity of the hippocampus major, but it only 
spread over the surface of the hippocampus major for about a fourth of the width of the 
latter. Both the concave and convex margins of the fimbria were free, so that it only 
adhered to the surface of the hippocampus to a slight extent. So far as could be seen, 
the fimbria became continuous with the lower end of the gyrus dentatus and the adjacent 
part of the gyrus hippocampi close to the uncus. 
The posterior cornu was not narrow and pointed towards its occipital end as in 
man. Indeed, it appeared more like a wide backward extension of the middle cornu, 
for at its commencement it was 2 ems. wide, and at this place the emanentia collateralis 
appeared as a large well-defined elevation indented anteriorly by the convex face of 
the hippocampus major, but these two objects were separated from each other by the 
upward extension of the fissure already referred to on the floor of the middle cornu. 
On the mesial aspect of the cornu, and above the eminentia collateralis, there were two 
strongly defined convex ridges, the one above the other. Both of these ridges appeared 
from under cover of the hinder end of the corpus callosum, with which they were con- 
tinuous. The lower of the two was directed outwards and backwards. It descended 
to the floor of the cornu, and ceased to be an elevated object immediately behind the 
eminentia collateralis. As already indicated in an earlier part of my description, this 
elevation corresponded to the general position of the calcarine fissure on the inferior 
aspect of the occipital lobe of the cerebrum, and for that reason I have regarded the 
elevation just described as the calear avis or hippocampus minor. The upper of the 
two elevated ridges seen in the posterior cornu was the larger at its commencement, 
but it narrowed down rapidly, and disappeared on the floor of the cornu behind the 
calcar avis. This object may be taken as the bulb of the posterior cornu. Fig. 4 
shows these two structures in relation to the calcarine fissure, and it will be observed 
that the bulb of the cornu has a more direct relation to the calcarine fissure than the 
ealcar avis has. The posterior cornu extended backwards for a distance of 2 cms., and 
terminated in a blind rounded extremity which, from the size of the eminentia collater- 
alis, appeared to dip downwards. Certainly it showed no tendency to bend towards 
the mesial surface of the occipital lobe. 
The body of the lateral ventricle was roofed over, as already stated, by the tapetal 
fibres of the corpus callosum. On its floor the following structures were noted :— 
Anteriorly the nucleus caudatus, which was particularly well shaped ; to the mesial 
side of its tailed part, there was the choroid plexus of the velum interpositum, and this 
choroid plexus was spread out sufficiently to entirely conceal the teenia semicircularis ; 
behind the choroid plexus there lay the widely expanded lateral half of the body of 
