172 THE DESCENT OF MAN. 



to have a trifling case of reversion to a progenitor in whom 

 the forehead had not as yet become quite naked. 



It is well known that the hair on our arms tends to con- 

 verge from above and below to a point at the elbow. This 

 curious arrangement, so unlike that in most of the lower 

 mammals, is common to the gorrilla, chimpanzee, orang, 

 some species of Hylobates, and even to some few American 

 monkeys. But in Hylobates agilis the hair on the forearm 

 is directed downward or toward the wrist in the ordinary 

 manner; and in H. lar it is nearly erect, with only a very 

 slight forward inclination; so that in this latter species it 

 is in a transitional state. It can hardly be doubted that 

 with most mammals the thickness of the hair on the back 

 and its direction is adapted to throw off the rain; even the 

 transverse hairs on the fore legs of a dog may serve for this 

 end when he is coiled up asleep. Mr. Wallace, who has 

 carefully studed the habits of the orang, remarks that the 

 convergence of the hair toward the elbow on the arms of 

 the orang may be explained as serving to throw off the 

 rain, for this animal during rainy weather sits with its 

 arms bent and with the hands clasped round a branch or 

 over its head. According to Livingstone, the gorilla also 

 *^sits in pelting rain with his hands over his head.^^* If 

 the above explanation is correct, as seems probable, the 

 direction of the hair on our own arms offers a curious 

 record of our former state; for no one supposes that it is 

 now of any use in throwing off the rain; nor in our present 

 erect condition is it properly directed for this purpose. 



It would, however, be rash to trust too much to the 

 principle of adaptation in regard to the direction of the 

 hair in man or his early progenitors; for it is impossible to 

 study the figures given by Eschricht of the arrangement of 

 the hair on the human foetus (this being the same as in the 

 adult) and not agree with this excellent observer that other 

 and more complex causes have intervened. The points of 

 convergence seem to stand in some relation to those points 

 in the embryo which are last closed in during development. 

 There appears, also, to exist some relation between the 

 arrangement of the hair on the limbs and the course of the 

 medullary arteries, f 



* Quoted by Reade, "The African Sketch Book," vol. i, 1873, p. 

 152. 

 f On the hair in Hylobates, see " Nat, Hist, of Mammals," by C. L. 



