200 The Descent of Man. Part I. 



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

 citation from him. 



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

 " come very close tn man in their (irg.misation, 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 probiibly 

 " would ever have disputed the view of Linnaeus, that man should be 

 " placed, Tnerely as a peculiar species, at the hrad 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 differetioes which re illy exist. So it is with the brains. The 

 " bi-ains of man, the orang, the chimpanzee, the gorilla, in .spite of all 

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

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



There remains, then, no dispute as to the resemblance in fundamental 

 characters, between the apjs 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 ditferences. It is admitted that the man's 

 cerebral hemispheres are absolutely and r( datively larger than those of 

 the orang and chimpanzee ; that his frontal lobes are leas 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 rule, in man, the 

 temporo-occipital or "external perpendicular" fi&sure, which is usually 

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

 But it is also clear, tliat none of these dirterences constitutes a sha; p 

 demarcation between tlie 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 :" 



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

 " the hemisphere, but, in others, 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-tenlhs of an inch out- 

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

 " ou'er surface of the hemisphere. The imperfect definition of this fissure 

 " in thema-iority of human brains, as compared with its remarkable dis- 

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

 " the former, of certain superficial, well marlJed, secondaiy convolutions 

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

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

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



The obliteration of the external perpendicular fissure of Gratiolet, 

 thei'efore, 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 biain. For, in the chimpanzee, the more or less extensive oblilera- 

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

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



" 'Convolutions of the Human Cerebrum Topographically Cnnsiie;ei). 

 1866, p. 12. 



