834 PROFESSOR DAVID HEPBURN ON 
the anterior aspect of the genu from the surrounding convoluted surface, commenced 
at the locus perforatus anticus, which to a considerable extent encroached upon the 
mesial aspect of the hemisphere and presented itself in front of the lamina terminalis 
below the genu of the corpus callosum. Several shallow extensions of the callosal 
sulcus, in relation to the anterior half of the corpus callosum, ran forwards and upwards 
into the superincumbent convolution, thereby complicating the appearance of that gyrus. 
The sulcus cruciatus was visible upon this aspect of the frontal lobe, and here it 
divided into several branches, of which the hindermost was the longest. 
There also appeared on this surface the fissure which I have accepted as the fissure 
of Rolando, and it extended from the superior margin of the hemisphere downwards 
and backwards to a point almost half way to the dorsal surface of the corpus callosum. 
The calloso-marginal sulcus was much interrupted by the invasion of other fissures, 
so that 1t was composed of not only the fissure on the dorsal aspect of the callosal 
gyrus, but also of a branch from the cruciate sulcus anteriorly, and a branch from a 
fissure situated posterior to the callosal gyrus (fig. 2). 
The mesial aspect of the occipital lobe was reduced to comparatively small dimen- 
sions in comparison with the size of the hemisphere, a condition which resulted from 
the fact that occipital structures, which in a human brain of corresponding magnitude 
would have been visible on its mesial face, were in this seal’s brain turned to the 
inferior or cerebellar aspect of the occipital lobe. For this reason there was very 
considerable difficulty in selecting a fissure which could be regarded as homologous 
with the internal parieto-occipital sulcus. As the result of a later dissection, which 
determined the position of the calcarine fissure, I concluded that the fissure which is 
immediately posterior to the callosal gyrus, and whose course is upwards and forwards 
towards the supero-mesial border of the hemisphere (fig. 2), should be regarded as the 
internal parieto-occipital sulcus. Apparently this is the splenial fissure of some authors. 
The callosal gyrus started by rising gradually from the locus perforatus anticus 
immediately below the genu of the corpus callosum. It ran forwards, and growing 
larger as it proceeded it wound round the anterior end of the genu, forming several 
well-marked folds situated between the callosal and cruciate sulci. Thereafter it passed 
backwards in a straighter or less elaborate form above the posterior two-thirds of the 
corpus callosum and between the callosal and calloso-marginal sulci. Posterior to the 
splenium it turned abruptly towards the basal aspect of the hemisphere, constituting 
what is known in human anatomy as the isthmus of the limbic lobe. Subsequently 
(fig. 3) it curved along the infero-lateral aspect as the hippocampal gyrus, which 
steadily expanded as it proceeded forwards to terminate in a wide flattened extremity 
situated close behind the locus perforatus anticus, but separated from it by the basal 
segment of the Sylvian fissure. In a later stage of the dissection the wncus was found 
in connection with the hippocampal gyrus. 
So far, therefore, as the essential elements which enter ne its formation are 
concerned, the limbic lobe in all its parts was fully represented ; and only at its frontal 
