124 PROFESSOR DAVID HEPBURN ON 



sulcus. The general arrangement of their surface suggested the possibility of the 

 rhinal fissure being the foundation for the more elaborate fissures which characterise 

 the orbital surface of the higher brains. 



The olfactory tract presented two distinct roots, separated from each other by a 

 large area of the locus perforatus anticus. Of these, the mesial root came into view 

 from the mesial surface in relation to the anterior end of the callosal gyrus of the 

 limbic lobe. The lateral root emerged from under cover of the expanded end of 

 the hippocampal gyrus. Closely adhering to the locus perforatus anticus, these 

 roots converged and fused to form the olfactory tract, which occupied and moulded 

 itself to the olfactory sulcus. 



In all my adult specimens the olfactory bulb had been broken off, so that I am 

 not able to state its size, frontal relations, etc. ; but it was present in the young specimen 

 as an ovoid enlargement 17 mm. in length and 6 mm. in breadth. It turned upwards 

 upon the frontal surface of the hemisphere, to which it was closely applied. 



Behind the fissure of Sylvius, the basal surfaces of the occipito-temporal lobes were 

 much more expanded in the lateral direction than is the case in the primate brain ; 

 and, as a consequence, convolutions and sulci which are not found on this aspect in 

 the human brain were visible in the brain under consideration. At the same time, 

 it presented sulci which do not occur in a human brain, and therefore it is not easy 

 to suggest a nomenclature for some of these sulci, nor to be quite certain that they 

 should be accepted as providing boundaries between the occipital and temporal sections 

 of the surface. 



The dentate and collateral sulci, situated respectively on the mesial and lateral 

 aspects of the hippocampal gyrus, were distinctly indicated. Towards the hinder end 

 the collateral sulcus was interrupted by a bridging gyrus, behind which the sulcus 

 corresponded to the general position of the eminentia collateralis in the lateral 

 ventricle, as was afterwards revealed by dissection. Further, with the same part of 

 the sulcus, i.e. posterior to the annectant gyrus, just mentioned, other two well-marked 

 sulci communicated. Of these, one was directed backwards towards the occipital end 

 of the hemisphere, and the other diverged backwards and outwards towards the 

 infero-lateral margin of the hemisphere in its occipital area. Thus a large segment 

 of the occipito-temporal surface, situated between the collateral sulcus and the infero- 

 lateral margin of the hemisphere, was divided into three wedge-shaped gyri whose 

 bases were directed towards the infero-lateral margin and whose apices converged 

 towards the annectant gyrus above referred to. Indeed, this annectant gyrus connected 

 the anterior and the middle of the three wedge-shaped gyri with the middle portion 

 of the hippocampal gyrus. The posterior one of these three wedges presented a free 

 apex, but the surfaces of each of the three showed indications of further subdivision 

 by additional sulci. 



The callosal and hippocampal gyri were united to each other by a narrow gyrus 

 which curved round behind the splenium of the corpus callosum and the crura cerebri. 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 836.) 



