VERTEBRATES: BACKBONE AND BRAIN 95 



human skull of small cranial capacity and large jaws, 

 in which the cranium has been pressed back and the 

 jaws crowded forward and slightly upward. 



The weight of the brain in proportion to that of the 

 body has been considered as of great importance, and 

 within certain limits this is undoubtedly correct. 

 Thus, according to Leuret, the weight of the brain is 

 to that of the whole body : In fish, 1 : 5,668 ; in reptiles, 

 1 : 1,320 ; in birds, 1 : 212 ; in mammals, 1 : 186. These 

 figures give the averages of large numbers of observa- 

 tions and have a certain amount of value. But within 

 the same class the ratio varies extraordinarily. Thus 

 the weight of the brain is to that of the whole body : 

 In the elephant, 1 : 500 ; in the largest dogs, 1 : 305 ; in 

 the cat, 1 : 156 ; in the rat, 1 : 76 ; in the chimpanzee, 

 1 : 50 ; in man, 1 : 36 ; in the field-mouse, 1 : 31 ; in the 

 goldfinch, 1 : 24. 



From this series it is evident that the relative 

 weight of the brain is no index of the intelligence of 

 the animal. Indeed if the brain were purely an organ 

 of mind, there is no reason that it should be any 

 larger in an elephant than in a mouse, provided they 

 had the same mental capacity. As animals grow 

 larger the weight of the brain, relatively to that of the 

 body, decreases, and considering the size of man it is 

 remarkable that it should form so large a fraction of his 

 weight. Still the fraction in the chimpanzee is not so 

 much smaller. It is still possible that this fraction is 

 above the normal for the chimpanzee, for some of the 

 observations may have been taken on animals which 

 had died of consumption or some other wasting dis- 

 ease. I have not been able to find whether this pos- 

 sibility of error has been scrupulously avoided. 



