VERTEBRATES: BACKBONE AND BRAIN 97 



book which I cannot too highly recommend to you all, 

 " It may be doubted whether a healthy human adult 

 brain ever weighed less than 31 or 32 ounces, or that 

 the heaviest gorilla brain has ever exceeded 20 ounces. 

 The difference in weight of brain between the highest 

 and the lowest men is far greater, both relatively and 

 absolutely, than that between the lowest man and the 

 highest ape. The latter, as has been seen, is repre- 

 sented by 12 ounces of cerebral substance absolutely, 

 or by 32 : 20 relatively. But as the largest recorded 

 human brain weighed between 65 and 66 ounces, the 

 former difference is represented by 33 ounces abso- 

 lutely, or by 65 : 32 relatively." 



But there is another characteristic of the brain 

 which seems to bear a close relation to the degree of 

 intelligence. The surface of the human brain is not 

 smooth but covered with convolutions, with alternating 

 grooves or sulci, which vastly increase its surface and 

 thus make room for more gray matter. Says Gratio- 

 lett : " On comparing a series of human and simian 

 brains we are immediately struck with the analogy ex- 

 hibited in the cerebral forms in all these creatures. 

 There is a cerebral form peculiar to man and the apes ; 

 and so in the cerebral convolutions, wherever they ap- 

 pear, there is a general unity of arrangement, a plan, 

 the type of which is common to all these creatures." 

 Professor Huxley says : " It is most remarkable that, as 

 soon as all the principal sulci appear, the pattern ac- 

 cording to which they are arranged is identical with 

 the corresponding sulci in man. The surface of the 

 brain of the monkey exhibits a sort of skeleton map of 

 man's, and in the man-like apes the details become 

 more and more filled in, until it is only in minor 

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