LECTURE vr. 165 



ficant in the highest degree, when the question apphes to the 

 comparison of the cerebral convolutions in man and the ape. 

 In fact : — 



1. In the chimpanzee the posterior lobe is large and the 

 operculum well marked. The upper transition convolution is 

 wanting, the second is covered. 



2. In the orang the posterior lobe is moderate and its oper- 

 culum imperfect. The superior transition convolution is large 

 and superficial, the second covered. 



3. In man the posterior lobe is much reduced, the oper- 

 culum is absent. The two superior transition convolutions 

 are large, undulating, and both superficial. 



" Does not this regular gradation tell its own tale ? " 



The question does not turn here on the two superior transi- 

 tion convolutions, which are both in apes and men superficial 

 and uncovered ; but on the two superior, and not even on 

 both of them, but on the second, for the superior is in the 

 orang as in man, uncovered, superficial, and free. Then there 

 is the operculum, which, though imperfect, exists in the orang. 

 I now write in my note book : Man is distinguished from the 

 ape by the absence of an imperfect operculum and by the 

 second transition convolution being uncovered. I may here 

 apply Wagner's observation that we can hardly consider 

 insignificant variations, as the second flis de passage, which, 

 in some cases, as Dareste (another convolution student) 

 maintains, may in the same individual differ in both hemi- 

 spheres, as characteristic marks of man. But I console myself 

 by studying my Gratiolet, and I read of the devil's ape (ateles 

 Beelzebuth) . " We easily recognise the posterior lobe, it is 

 of moderate size ; anteriorly its limits are badly defined. The 

 external vertical fissure is in fact obliterated by the develop- 

 ment of the transition convolutions, which are very large and 

 all superficial. 



" This circumstance is most important, as, hitherto, we have 

 only found it in man." 



But is it not remarkable that Gratiolet, in the second part 

 of his Essay, which treats of the American apes (the devil's 

 and the capuchin ape belong to the new world), establishes 



