104 INITIATIVE IN EVOLUTION 



The back and the front surfaces of the trunk afford the two 

 best and most instructive fields of study, for the forces which act 

 upon them are of a simple kind, and may be traced upwards from 

 the lemurs to man as in the case of th e forearms . The three drawings 

 (Fig. 41) represent the backs of a lemur, chimpanzee and man, most 

 of the details of the hair being omitted and their place taken by 

 thick dark arrows which show the line of the different hair-streams. 

 This diagrammatic method will make any misunderstanding of 

 the main facts impossible. 



The lemur has on the back of its neck a forward or headward 

 slope of hair and this passes on to the head itself, and on the back 

 of the trunk, as the arrows show, there is no departure from the 

 normal arrangement of the lower mammals. The lemur, therefore, 

 requiies neither further description nor explanation. 



The ape shows no material change in this region from the 

 arrangement of its lemur or monkey ancestor, in spite of the greater 

 proportion of its life which is spent in the upright posture ; indeed, 

 this is what one would expect. 



Hair of the Back of Man. 



When the hair on the back of man is examined a remarkable 

 change from the patterns of any of his known or supposed ancestors 

 is found. It is by no means easy to trace the course of the hairs 

 on the human back. A young, hair}' and dark-haired person 

 gives much the best field, and a lens may be necessary. In older 

 subjects the hair is often so much worn away by friction that the 

 direction can no longer be followed. Suffice it to say that the 

 examination, though somewhat difficult, can well be carried out 

 if the proper conditions are observed ; and that it bears out the 

 results which have come from the corresponding examination of 

 infants. The arrangement is congenital. 



From the neck the hair passes on each side nearly downwards, 

 and in the middle directly downwards in a narrow stream between 

 the two muscular borders of the vertebral furrows, and continues 

 in this normal direction to the end of the spinal region. It will 

 be seen that below the two upper arrows there are three levels of 

 arrows, the first with one, the second with two, and the third with 

 one, on each side of the surface of the back. At the level of the 

 shoulder -joints the side-streams curve upwards towards the spine 

 and join the central stream ; at the second the direction is rather 

 more upwards before it curves inwards and downwards to the 

 vertebral furrow ; at the third the streams curve slightly upwards 

 and towards the middle-line and coalesce with the other streams. 



