102 INITIATIVE IN EVOLUTION 



of these attitudes contributes to a very well-marked change of 

 the hair on the under surface of his fore arms, to use a convenient 

 human term, one which carries us back to the story of man and the 

 apes when their fore arms were discussed. On this surface, from 

 the mechanical conditions involved, a new force, that of sliding 

 pressure, comes into play. The skin here is very loose, as indeed 

 it is in the greater part of his body, which may almost be said to 

 form one large subcutaneous bursa. The weight of the fore part 

 of his body and head acts downwards and forwards, and thus opposes 

 the normal or downward course of the hair on the limb, such as 

 one sees on the upper surface of his fore arm. The resultant of 

 these two forces has the effect of acting against the normal slope, 

 and a reversed direction of the hair is produced very much like 

 that which is seen in many monkeys and in a small area in man. 

 This is shown in Fig. 39, which appeared in the small book 1 , to 

 which reference has been made, and it is confined to the part of 

 the limb where the sliding pressure is seen to act. In this feature 

 again there is a record of his testing habits, and, of course, the time 

 he spends in the fourth attitude with his chin resting on his fore paws 

 contributes its share, the mechanical conditions being similar. 



This fourth attitude brings in another force of its own towards 

 the " make-up " of the dog's patterns of hair. When lying with 

 his head supported on his paws the lower part of his chest is closely 

 applied to the upper or flexor surface of the fore legs, and the long- 

 continued pressuie of the latter against the downward or normal 

 streams of hair on the chest leads to its slope being reversed. This 

 is shown in two wide patterns of the whorl, feathering and crest, 

 Fig. 40, resembling closely the corresponding patterns on the 

 chest of a horse. I had the opportunity many j^ears ago of examin- 

 ing in the Capitol Museum at Rome two fine sculptures of Molossian 

 hounds, when these matters of hair-arrangement were occupying 

 my attention, and was much struck with the fidelity with which 

 the ancient sculptor reproduced such small facts as the reversed 

 areas of hair in a dog. Phiz himself was not more true to Nature 

 in his delineation of the projecting hairs on the human eyebrows. 

 It should be added that the reversed hair in question occupies 

 only that part of the chest which is in contact with the fore limb. 

 If one cannot reckon any animal pedometers, to the credit of the 

 domestic dog I think one may fairly and metaphorically say that 

 his hairy coat gives an accurate mould of his habits. 



1 Use — Inheritance. 



