88 HISTORY OF THE HUMAN BODY 



with two lateral hairs on each side, or groups of seven with 

 three. Occasionally, as in the dog and cat, the plan becomes 

 partly obscured in the adult, but is evident during development, 



FIG. 22. Formation of friction ridges from single rows of epidermic 

 warts. [After Miss WHIPPLE.] 



(a) Midas rosalia (Brazilian monkey). Proximal portion of hypothenar pad. (b) 

 Midas rosalia. Apical pad. (c) Homo. Advanced fetus. Side of finger in tran- 

 sition region. The dotted lines indicate the position of sweat-glands. 



the three-hair group being definitely marked in the advanced 

 fetus. 



A still further corroboration of the former presence of scales 

 in mammals may be obtained from the study of the lower 

 surfaces of the paws, where, except in such extreme modifica- 

 tions as the ungulates, scales either still exist or have left a 

 permanent record in a peculiar configuration of the epidermis, 



