62 THE DESCENT OF MAN. 



respect to the lower animals, M. E. Lartet,* by comparing 

 the crania of tertiary and recent mammals belonging to 

 the same groups, has come to the remarkable conclusion 

 that the brain is generally larger and the convolutions are 

 more complex in the more recent forms. On the other 

 hand, I have shown f 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 genera- 

 tions, so that they have exerted their intellect, instincts, 

 senses and voluntary movements but little. 



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 se- 

 vere burn, have permanently modified the facial bones. In 

 young persons whose heads have become fixed either side- 

 ways or backward, owing to disease, one of the two eyes 

 has changed its position, and the shape of the skull has 

 been altered apparently by the pressure of the brain in a 

 new direction. \ I have shown that with long-eared rabbits 



must be lowered by the preservation of a considerable nnmber of in- 

 dividuals, weak in mind and body, who would have been promptly 

 eliminated in the savage state. On the other hand, with savages, the 

 average includes only the more capable individuals, who have lieen 

 able to survive under extremely hard conditions of life. Broca thus 

 explains the otherwise inexplicable fact, that the mean capacity of 

 the skull of the ancient Troglodytes of Lozere is greater than that of 

 modern Frenchmen. 



* * Comptes-rendus des Sciences," etc., June 1, 1868. 



f "The Variation of Animals and Plants under Domestication," 

 vol. i, pp. 134-129. 



X 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 in certain trades, such as that of a shoemaker, where 

 the head is habitually held forward, the forehead becomes more 

 rounded and prominent. 



