

OF THE ORA.NG UTA.NG. 17 



lower varieties of man, the reverse condition obtains. The 

 variability which we have seen to exist in the species chimpanzee 

 is no inconsiderable proof of its high relative rank in its own 

 order. 



But there is a second connecting bridge passing between the 

 occipital and the parietal lobes. This convolution is invariably 

 present, and invariably superficially placed in man ; it is as in- 

 variably absent in both the anthropoid apes. In man it is always 

 a large, easily recognisable structure ; and in cases such as those 

 which our fourth human brain may be taken to exemplify, or 

 exaggerate, it will be often found to send a branch, as it were, in 

 aid of the weakened superior bridge. The vacuity which in the 

 apes corresponds to what is invariably a convolution of importance 

 in man, may be seen in Fig. i, immediately posteriorly to 6 ; and 

 in Fig. 3, immediately below a. But this convolution, the ' deuxieme 

 pli de passage' of Gratiolet, absent without exception in the Old 

 World apes, and present equally invariably in man, is found also in 

 two New World monkeys, the Cebus capucinus 1 possessing it without, 

 the Ateles possessing it in company with its fellow 2 . 



There is yet a third structure — ' the lobule of the marginal con- 

 volution ' — to be treated of. In man it lies above the upper end of 

 the fissure of Sylvius; and it may not unfairly be represented in our 

 Fig. 1, by the convolution which lies immediately to the spectator's 

 left of 5. Of it M. Gratiolet speaks in the following language: 'Ge 

 lobule est particulier a l'homme et ne se retrouve ni dans l'orang 

 ni dans le chimpanze 3 .' But I find nowhere in M. Gratiolet's 

 work any repetition of this striking statement : indeed it loses a 

 good deal of its force, when we find the qualifying words ■ souvent 

 assez grand ' applied to this peculiarly anthropic lobule in the 

 sentence immediately preceding the one we have quoted. And in 

 the coloured diagrams, which speak so plainly, by their various 

 hues, of the varied relations in extent and arrangement which may 

 obtain among different brains, I find no separate colour assigned to 

 this peculiarly separable lobe. No such distinction is awarded to 

 them as there is to the bridging ' plis de passage ; ' which, never- 

 theless, are not asserted to be exclusively anthropic. These con- 

 siderations make me suspect that more weight has been attached to 

 M. Gratiolet's words, as above quoted, than he would have wished 



1 Gratiolet, 'Memoire,' 1854, p. 78. 2 Ibid. p. 76. 3 Ibid. p. 60. 



C 



