2 CHARLES MIDLO AND HAROLD CUMMINS 



In all primates and in some other mammalian orders, 

 especially marsupials, the skin of the palmar and plantar 

 surfaces (and of the ventral surface of the tail in several 

 New World monkeys) is distinctive in having a ridged or finely 

 pebbled surface, hairs and sebaceous glands being absent. 

 The pebbling (occurrence of islands, epidermal rings and 

 "warts" -Whipple) represents a less advanced structural 

 differentiation than does the presence of continuous epi- 

 dermal ridges. Among the chief objects of study in a com- 

 parative survey of dermatoglyphics are determinations of the 

 extent and distribution of areas presenting formed ridges 

 and analysis of the variable arrangements of these ridges. 

 Flexion furrows and other secondary folds are not elements 

 of the dermatoglyphics. 



In the majority of prosimians and in certain genera of 

 New World monkeys, there occur in both palm and sole more 

 or less extensive areas which lack ridges. Less frequently and 

 less extensively is that the case in the Old World monkeys, 

 while in higher primates the entire palmar and plantar sur- 

 faces are invariably continuously ridged, though often the 

 ridges within flexion furrows are ill-formed. It should be 

 noted, as emphasized by Whipple, that areas lacking formed 

 ridges (presenting only islands, rings or "warts") occur in 

 territories between pads or on their basal slopes. 



In areas presenting definitely formed ridges .there are 

 distinguished three fundamental types of configuration : open 

 fields, patterns and "vestiges". An open field is a succession 

 of ridges which are straight or only gently curved. A pattern 

 differs in that ridges are locally sharply recurved to form 

 definite figures or designs. Such patterns are here classed 

 under four main types: tented arches, loops, whorls and 

 S-patterns. These types have their parallels in the more 

 familiar patterns of the human finger tips, simple arches being- 

 excluded because they are open fields by definition. A vestige 

 is a departure from the typical arrangement of an open field, 

 its disarrangement of ridge courses suggesting a relation- 

 ship to a pattern, as if a pattern were nascent or degenerated. 



