DERMATOGLYPHICS IN PRIMATES 7 



DESCRIPTIVE MORPHOLOGY 



EPIDERMAL RIDGES 

 DISTBIBUTION AND FUNCTIONS 



Whipple devotes a large share of her study to a considera- 

 tion of the morphology and evolutionary history of epidermal 

 ridges, comparing her own findings with those of previous 

 workers, especially Blaschko (1884, 1887), Klaatsch (1888), 

 de Meijere (1894) and Reh (1894). The detailed construction 

 of single ridges and of their forerunners is of little immediate 

 interest, but their history among mammals provides an im- 

 portant orientation for interpreting the distribution of fully 

 formed ridges in primates. Whipple points to the occurrence, 

 on the summits of pads, of ridges in forms as low as mar- 

 supials, an edentate (Myrmecophaga) and some rodents (the 

 wood-rat Neotoma, and Sciurus). In prosimians (Galago and 

 Lemur) completed ridges are more extensive, but, according 

 to her, still limited to the surfaces of pads, while in most 

 simians the entire palmar and plantar surfaces are marked 

 continuously by formed ridges. The sequence of stages of 

 ridge evolution gives evidence that ridges are modified scales, 

 and Whipple ascribes their conversion to ridge structure to 

 factors associated with the functioning of contact surfaces. 

 She writes : 



"In ancient mammals the larger part of the surface of the 

 body was covered with imbricated scales. Each of these scales 

 or scale elements possessed, associated with it, a hair (or 

 hair-group) and a sweat gland, the position of each being- 

 constant with relation to the scale. In recent mammals the 

 scales occasionally persist, especially on tails and paws, show- 

 ing, however, more or less modification of the original type. 

 . . . Upon the ventral chiridial surface, there developed in the 

 early mammals or in the pre-mammalian forms, a definite 

 arrangement of walking pads in three rows. . . . Over the pad 

 surfaces which, because of their greater elevation, are brought 

 in contact with external surfaces, a highly specialized friction 

 skin is developed by the fusion into ridges of rows of modified 

 scales, characterized by the loss of hair and by the hypertrophy 



