82 THE DESCENT OF MAN 



The gradually increasing weight of the brain and skull 

 in man must have influenced the development of the sup- 

 porting spinal column, more especially while he was becom- 

 ing erect. As this change of position was being brought 

 about, the internal pressure of the brain will also have in- 

 fluenced the form of the skull; for many facts show how 

 easily the skull is thus affected. Ethnologists believe that 

 it is modified by the kind of cradle in which infants sleep. 

 Habitual spasms of the muscles, and a cicatrix from a severe 

 burn, have permanently modified the facial bones. In young 

 persons whose heads have become fixed either sidewise or 

 backward, owing to disease, one of the two eyes has changed 

 its position, and the shape of the skull has been altered ap- 

 parently by the pressure of the brain in a new direction. '* 

 I have shown that with long-eared rabbits even so trifling a 

 cause as the lopping forward of one ear drags forward almost 

 every bone of the skull on that side ; so that the bones on 

 the opposite side no longer strictly correspond. Lastly, if 

 any animal were to increase or diminish much in general 

 size, without any change in its mental powers, or if the 

 mental powers were to be much increased or diminished, 

 without any great change in the size of the body, the shape 

 of the skull would almost certainly be altered. I infer this 

 from my observations on domestic rabbits, some kinds of 

 which have become very much larger than the wild animal, 

 while others have retained nearly the same size, but in both 

 cases the brain has been much reduced relatively to the size 

 of the body. Now I was at first much surprised on finding 

 that in all these rabbits the skull had become elongated or 

 dolichocephalic; for instance, of two skulls of nearly equal 

 breadth, the one from a wild rabbit and the other from a 



^ Schaaffhausen gives from Blumenbaoh and Busch the cases of the 

 spasms and cicatrix, in "Anthropol. Revie-w, " Oct., 1868, p. 420. Dr. Jarrold 

 ("Anthropologia, " 1808, pp. 115, 116) adduces from Camper and from his 

 own observations, cases of the modification of the skull from the head being 

 fixed in an unnatural position. He believes that in certain trades, such as that 

 of a shoemaker, where the head is habitually held forward, the forehead 

 becomes more rounded and prominent. 



