144 



HARRIS HAWTHORNE WILDER. 



FIG. 5 



for each of the others, and where these folds come together there are formed Iriradii, 

 or centers from which folds radiate in three directions. 



Upon this original surface certain epidermic units (scales?) which are un- 

 doubtedly very primitive, and were there before the formation of pads and folds, 

 become definitely arranged in concentric circles over the pads, and in lines along 

 the folds. Nearly every stage in this rearrangement may be found by looking 

 over the more primitive mammals, especially marsupials and lemurs. The separate 

 rows of units tend to unite to form ridges, which possess an important function in 

 increasing the friction, and thus preventing slipping. 



In monkeys, Fig. 4, the pads and folds are flattened down to an approximately 

 level surface, but the arrangement of the ridges still indicates the former condition. 

 The relief has become a picture. 



In man, Fig. 5, the reduction in functional importance of these friction-ridges 

 allows all forms of degeneration, both in the individual patterns and in the ridges 



