200 The Descent of Man. Part I. 



differences between apes and men in this respect, I am glad to make a 

 citation from him. 



" That the apes, and especially the orang, chimpanzee and gorilla, 

 " come very close tj man in their organisation, much nearer than to any 

 " other animal, is a well known fact, disputed by nobody. Looking at 

 " the matter from the point of view of organisation alone, no one probably 

 •' would ever have disputed the view of Linnseus, that man should be 

 " placed, merely as a peculiar species, at the head of the mammalia and of 

 •* those apes. Both shew, in all their organs, so close an affinity, that the 

 " most exact anatomical investigation is needed in order to demonstrate 

 " those differences which redly exist. So it is with the brains. The 

 " brains of man, the orang, the chimpanzee, the gorilla, in spite of all 

 '* the important differences which they present, come very close to one 

 " another'' (1. c. p. 101). 



There remains, then, no dispute as to the resemblance in f nndamental 

 characters, between the ape's brain and man's; nor any as to the won- 

 derfully close similarity between the chimpanzee, orang and man, in 

 even the details of the arrangement of the gyri and sulci of the cerebral 

 hemispheres. Nor, turning to the differences between the brains of 

 the highest apes and that of man, is there any serious question as to 

 the nature and extent of these differences. It is admitted that the man's 

 cerebral hemispheres are absolutely a*nd relatively larger than those of 

 the orang and chimpanzee ; that his frontal lobes are less excavated by 

 the upward protrusion of the roof of the orbits ; that his gyri and sulci 

 are. as a rule, less symmetrically disposed, and present a greater number 

 of secondary plications. And it is admitted that, as a ride, in man, the 

 teinporo-occipital or " external perpendicular" fissure, which is usually 

 so strongly marked a feature of the ape's brain is but faintly marked. 

 But it is also clear, that none of these differences constitutes a sharp 

 demarcation between the man's and the ape's brain. In respect to the 

 external perpendicular fissure of Gratiolet, in the human brain, for 

 instance, Professor Turner remarks: 71 



<k In some brains it appears simply as an indentation of the margin of 

 " the hemisphere, but, in o'hers, it extends for some distance more or less 

 " transversely outwards. I saw it in the right hemisphere of a female 

 '• brain pass more than two inches outwards ; and in another specimen, 

 " also the right hemisphere, it proceeded for four-tenths of an inch out- 

 " wards, and then extended downwards, as far as the lower margin of the 

 11 ou^er surface of the hemisphere. The imperfect definition of this fissure 

 " in the majority of human brains, as compared with its remarkable dis- 

 " tinctness in the brain of most Quadrumaia, is owing to the presence, in 

 " the former, of certain superficial, well marked, secondary convolution? 

 " which bridge it over and conuect the parietal with the occipital lobe. 

 "The closer the first of these bridging gyri lies to the longitudhml 

 " fissure, the shorter is the external parieto-occipital fissure." (1. c. p. 12.) 



The obliteration of the external perpendicular fissure of Gratiolet, 

 therefore, is not a constant character of the human brain. On the other 

 hand, its full development is not a constant character of the higher 

 ape's brain. For, in the chimpanzee, the more or less extensive oblitera- 

 tion of the external perpendicular sulcus by " bridging convolutions," on 

 one side or the other, has been noted over and over again bv Prof 



"©* 



T1 'Convolutions of the Human Cerebrum Topographically Considered, 

 1866, p. 12. 



