Chap. IT.] MANNER OF DEVELOPMENT. 141 



other hand, I have shewn 73 that the brains of domestic 

 rabbits are considerably reduced in bulk, in comparison 

 with those of the wild rabbit, or hare ; and this may be 

 attributed to their having been closely confined during 

 many generations, so that they have exerted but little 

 their intellect, instincts, senses, and voluntary movements. 

 The gradually-increasing weight of the brain and 

 skull in man must have influenced the development of the 

 supporting spinal column, more especially while he was 

 becoming erect. As this change of position was being 

 brought about, the internal pressure of the brain will, 

 also, have influenced the form of the skull ; for many facts 

 show how easily the skull is thus afteeted. Ethnologists 

 believe that it is modified by the kind of cradle in which 

 infants sleep. Habitual spasms of the muscles and a cic- 

 atrix from a severe burn have permanently modified the 

 facial bones. In young persons whose heads from disease 

 have become fixed either sideways or backward, one of 

 the eyes has changed its position, and the bones of the 

 skull have been modified; and this apparently results 

 from the brain pressing in a new direction. 74 I have shown 

 that with lono;-eared rabbits, even so trifling a cause as 

 the lopping forward of one ear drags forward on that side 

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

 opposite sides 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 



73 ' The Variation of Animals and Plants under Domestication,' vol. i. 

 pp. 124-129. 



74 Schaaffhausen gives from Blumenbach and Busch, the cases of the 

 spasms and cicatrix, in ' Anthropolog. Review,' 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 certain 

 trades, such as that of a shoemaker, by causing the head to be habitually 

 held forward, makes the forehead more rounded and prominent. 



