OF THE ORANG UTANG. 19 



symmetrical in the chimpanzee than in the orang, but it is not 

 larger in size. Both ascending convolutions are a little more 

 simple in the chimpanzee than in the orang. 



Having arrived at our last head — that, namely, of such differ- 

 entiae as are detectable by dissection only — we will proceed to lay 

 them before the reader in the shape of a short account of the 

 dissection which disclosed them. 



The right cerebral hemisphere was removed down to the level of 

 the corpus callosum, as seen in Fig. 4. At a point relatively much 

 further distant from its posterior edge, 14, than is the case in man, 

 w T e see the internal perpendicular fissure, 16. Posteriorly again to 

 this fissure, and running nearly parallel with it, we see a second, 

 1 7, the ' scissure des hippocampes ' of M. Gratiolet. Corresponding 

 with this indentation, we have within the cavity of the ventricle 

 an eminence, 19, the lesser hippocampus, bounded by an arm or 

 creek running up, 18, along its outer surface from the central 

 ventricular expanse. This arm or creek was called, by another 

 metaphor than those we have used, the third cornu of the lateral 

 ventricle, in the phraseology of the old anatomists. The large 

 smooth headland into which the hippocampus swells at 19, justi- 

 fies the expression we find at page 16 of M. Gratiolet's work, 

 ' L'anfractuosite d'ergot . . . qui est plus evidente encore dans les 

 Singes que dans V Homme, In the brain of a cercopithecus now 

 before us, its proportions are very much larger. The width, of this 

 third cornu was at its commencement three-eighths of an inch ; and 

 the similar cavity in a human brain examined at the same time 

 was of the same width. But the cavity narrows much more 

 rapidly in the orang than in man ; and before reaching its termi- 

 nation, at a distance of one inch from its commencement, it be- 

 comes almost a linear cavity; but, as our figure shows, the 

 distinctness of its limiting walls and the continuity of its lining 

 membrane were unambiguously visible up to its very extremity. 

 The length of this third cornu is as great absolutely and relatively, 

 therefore much greater in the cercopithecus than in the orang. 

 In the human brain it was but half an inch longer than in the 

 orang, scooped out though it was in a posterior lobe relatively very 

 much longer. Neither in the cercopithecus, nor in the orang, does 

 the bourrelet or posterior rounded edge of the corpus callosum 

 extend nearly so far back as to allow us to take it as 'the best 



c a 



