336 MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 



parieto-occipital from the calcarine fissure, Ca. It has been asserted that this 

 separation of the parieto-occipital from the calcarine is a characteristic of the Simian 

 as distinguished from the human brain, and that in Man the parieto-occipital is 

 directly continuous with that fissure. Huxley, however, has shown that in the 

 brain of A teles pani sens the parieto-occipital and the calcarine join each other, and 

 he says that the inferior internal//?' de passage is absent in this monkey. Bischoff 

 claims, however, that it is present in Ateles* only pushed down and concealed in the 

 depths of the fissure. He also describes the same condition as occurring in Hylobates; 

 but in all the monkeys with a few exceptions, the parieto-occipital is completely 

 separated from the calcarine. Bischoff states, and with this I agree, that this 

 gyrus is always present in the brain of Man but that it is deeply sunk within the 

 depths of the parieto-occipital fissure. Ecker also describes it as represented in Man 

 by a deeply concealed convolution under the name of the gyrus cunei. In A teles 

 ater, PI. XXXVII, fig. 17, the parieto-occipital does not communicate with the 

 calcarine as found by Huxley in Ateles paniscus, but is distinctly separated by a 

 bridging gyrus, 1 . The confluence of the parieto-occipital with the calcarine fissure is 

 a characteristic which is not always found in the human brain, PI. XLII, fig, 2. 

 This represents the negro brain in which so many ape-like peculiarities have 

 been pointed out. The gyrus, 1, can be seen distinctly extending from the cuneus, 

 entirely superficial and completely separating the two fissures precisely as occurs in 

 the brain of the apes and monkeys. As far as 1 am aware this is the first human 

 brain in which this superficial and ape-like development of the gyrus cunei has been 

 observed, and this, in connection with the many other ape-like peculiarities previously 

 pointed out, stamp it as probably the most Simian-like of human brains yet figured 

 and described. A thorough study of a large number of negro brains, as we have 

 already remarked, would undoubtedly throw much light upon the comparison of the 

 ape and human brain and render interesting many points which at present appear 

 unimportant and obscure. 



Nothing of special interest is determined regarding the remaining pits de passage, 

 on the external surface, by a comparison of the human and ape brain. 



The true significance of the pits de passage seems to me not to have been 

 pointed out by previous observers, and 1 shall now endeavor to explain their 

 morphological relations to the type of convolutional configuration as developed in 

 this paper. 



In describing the development of the superior external pli de passage we made 

 mention of the fact that Huschke called this gyrus the obere Zug der hintere Central- 

 windung. He included the superior parietal with the posterior central convolution 

 under one name. 1 believe this is the correct view, and that the so-called plis de 

 passage are nothing but the posterior extremities of the occipito-frontal and the 

 oceipito-temporal convolutions, which, checked in their development by the evolution 

 of the occipital lobe in the Primates, lie concealed in the majority of them by the 

 overhanging operculum, whilst in the higher forms, through a renewed growth in this 

 region, as Ave have seen in the case of the convolution, 2, the}' finally reach the surface, 



