126 PROFESSOR DAVID HEPBURN ON 



Another unexpected result was, that at the level mentioned, viz. about 4 mm. 

 above the corpus callosum, the section opened into the cavity of the lateral ventricle, 

 which therefore rose to a higher level than the mesial surface of the corpus callosum, 

 and consequently there must be a corresponding deviation from the horizontal direction 

 of those fibres of the corpus callosum which form the roof structures in relation to the 

 body of the cavity of the lateral ventricle. This upward extension of the ventricle, 

 taken in conjunction with the large size of the convolutions as indicated by the depth of 

 the fissures, shows that notwithstanding its superficial dimensions the brain of the seal 

 falls considerably short of a human brain of similar size as regards the amount of grey 

 and white matter. 



In addition to what has already been stated with regard to the corpus callosum, the 

 following additional facts may be noted. The mesial faces of the two hemispheres were 

 so closely in apposition that opposing gyri practically interlocked with each other, and 

 therefore the dorsal surface of corpus callosum was entirely concealed. When this 

 surface was exposed it showed feeble striae longitudinales mediates and still feebler 

 laterales. The cingulum was present, but much smaller than the size of the surrounding 

 gyri led me to anticipate. The forceps major and. forceps minor were easily dissected 

 and were of characteristic appearance. 



On removing the roof of the lateral ventricle and of its cornua I was impressed by 

 the apparent simplicity of the basal ganglia, which were large, and at the first glance 

 suggested strongly such appearances as one is familiar with in the human brain. Taking 

 into consideration the somewhat elaborate and intricate condition of the convolutions 

 of the pallium, the simple nature of basal objects was remarkable. The anterior or 

 frontal cornu of the lateral ventricle was very shallow. Its course was outwards and 

 forwards into the substance of the frontal lobe, where it terminated in a blind recess. 

 Its relations to the septum lucidum and to the caput of the nucleus caudatus were 

 similar to the arrangements seen in the human brain. 



The middle or descending cornu likewise followed the human plan in its chief 

 features and direction. On its floor there were the clioroid plexus, theftmbria hippo- 

 campi, and the hippocampus major terminating in the pes hippocampi. The choroid 

 plexus was continuous with the pia mater of the dentate sulcus, and thus, as in man, the 

 termination of this cornu was situated on the lateral aspect of the crus cerebri and closed 

 by the ependyma ventriculorum. The choroid plexus, however, was wider than in man, 

 and spread itself out so as to form a vascular sheet which separated the objects in the 

 roof of this cornu from the other structures on its floor. Further, the hippocampus 

 major and the fimbria, with the overlying choroid plexus, were pressed upwards against 

 the roof of the cornu, where they adapted themselves to a deep furrow which was 

 bounded mesially by the optic tract and laterally by the tail of the caudate nucleus. 

 Again, on its convex margin the hippocampus major was separated from the Jiuor of 

 the cornu by a deep fissure which almost completely detached this object from the floor 

 of the cornu. Indeed, the connection between the hippocampus major and the floor of 



(BOY. soc. EDIN, TRANS., VOL. XLVIIL, 838.) 



