THE AX ATOMY OF THE WEDDELL SEAL. 127 



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 pe.t 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 fiinliria 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 cornn 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 cms. wide, and at this place the eminentia collateral/* 

 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 calcar avis or hippocampus minor. The v.pper 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 l>>t/l> 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 

 calcar avis has. The posterior cornu extended backwards for a distance of _' ems., and 

 terminated in a blind rounded extremity which, from the size of the eminentia collater- 

 alis, appeared to dip downwards. Certaiidy 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 <-<ui<ltns. which was particularly \\rll 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 tji-nia semicircularia ; 

 behind the choroid plexus there lay the widely expanded lateral half of the body of 



(BOY. SOC. KDIN. TRANS., VOL. XI.VIII., 839.) 



