146 THE SENSE OF TOUCH IN ANIMALS 



drawings illustrate. It is here maintained that these three 

 broad divisions of pattern are not fortuitous variations, and are 

 not unconnected with function, but are adaptations subserving 

 the sense of touch. The first change of arrangement of the 

 ridges is that by wliich they become grouped in elhpses on the 

 terminal phalanges of Didelphys azarce, and this type is found 

 throughout the Primates as far as the Anthropoid Apes, with an 

 occasional appearance of a loop in certain digits, e.g., in the 

 Chacma baboon. The next type of departure from the longi- 

 tudinal, obhque, and transverse arrangements shows an arched 

 shape of the ridges, and the first species in which arches have 

 been found are : Cercolepes caudivolvulus, below Primates and 

 Chrysothrix sciurea among them. From this form onwards to 

 man, arches are found in various digits and palmar and plantar 

 surfaces. A further development of the arch type takes place 

 by which loops are formed, as in the footpads in Lemur brunneus, 

 and are abundant in all the Primates above the Lemurs. The 

 most highly developed of the departures from a simple type 

 are whorls, which may be ovate or circular, the earhest instances 

 being found in the hand of Lemur catta among Primates. It 

 will be shown by illustrations from this series of drawings, that a 

 loop is a further development of an arch, and a whorl a further 

 development of a loop. A few species will be chosen for the 

 purpose of demonstrating this point. 



Lemur brunneus (Fig. 13) shows arches on the interdigital 

 eminences of the hand, and no whorl. 



Lemur catta (Fig. 15), arches and five marked whorls on the 

 palm. L. brunneus arches on the sole. L. catta, a much more 

 extensive series of arches on the sole, all the patterns of the 

 former being simpler than those of the latter. This fact agrees 

 with the generally higher development of the walkmg power 

 and of the form of the hand and foot in L. catta. 



Chrysothrix sciurea (Fig. 21) has on the phalanges good 

 illustrations of arches on four digits and loops on one. 

 The palmar surface presents well-marked loops on the distal 

 and arches on the proximal portion of the thenar eminence, 

 thus showing the transition from arch to loop on one area. 



