120 PROFESSOR DAVID HEPBURN ON 



whose lower end will be seen resting upon the fronto-parietal operculum of the insula, 

 and I have marked it by this name in fig. 1. In this respect my drawing and its 

 interpretation are more in agreement with MURIE'S * account of the sea-lion, although 

 in his drawing the fissure of Rolando is represented as much more extensive than it 

 appears to be in the Weddell seal. 



TURNER describes the cruciate fissure of the elephant seal as seen from the front and 

 not from the norma verticalis, and states that " a large sigmoid gyrus was bent around 

 its outer end." To some extent this description would apply to the Weddell seal, 

 although in the latter the cruciate fissure was visible from the norma verticalis, but it 

 was much more effectively seen from the norma frontalis, while its outer end was 

 blocked by an arched gyrus (fig. 1). 



I could nob find any satisfactory evidence of a homologue for the external parieto- 

 occipital fissure, and therefore no fixed indication of a limit between the parietal and 

 occipital lobes of the cerebrum on its lateral aspect, or between the occipital and 

 tempero-sphenoidal lobes on the same aspect, for the reason that these areas were freely 

 connected with each other by annectant gyri. 



The Convolutions on the Lateral Surface. 



The frontal lobe having been delimited in the manner described, its convolutions 

 resolved themselves into a pre-central (ascending frontal) ; the frontal contribution to 

 the opercula of the insula ; and two or three short convolutions running forwards from 

 the pre-central convolutions towards the sulcus cruciatus. 



The elongation of these short convolutions in a forward, i.e. frontal, direction would 

 have the effect of forcing the sulcus cruciatus forwards and downwards towards the roof 

 of the orbit, and would thus bring the cruciate fissure into position as a kind of 

 boundary line between the frontal and orbital aspects of the frontal lobe. It appears 

 to me that the blunt frontal end of the brain of the Weddell seal is due in some 

 measure to the presence of convolutions, which in the human brain would be found in 

 relation to the roof of the orbit. Further, in the human brain there may sometimes be 

 seen a fissure which runs transversely from the pallial fissure across the frontal lobe 

 and close above the orbital margin of the hemisphere. In my opinion this is a fissure 

 which may fairly be regarded as corresponding with the sulcus cruciatus. 



In the figure given by MURIE, and already referred to several times, there is, on the 

 frontal side of the fissure which is marked "Rolando," a convolution named in three 

 places as the antero-parietal convolution (AP) ; and I cannot but think that this was an 

 unfortunate term to introduce at such a place so long as the fissure of Rolando is 

 accepted as a boundary line between the frontal and parietal lobes of the highly 

 elaborated brain of man. 



From the fissure of Rolando (fig. l), and beginning at a point about its middle, a 

 well-marked fissure ran backwards towards the occipital end of the hemisphere. This 



* MURIE, loc. cit., pi. Ixxviii., fig. 40. 

 (BOY. soc. EDIN. TRANS., VOL. XLVIII., 832.) 



