116 CHARLES MIDLO AND HAROLD CUMMINS 



Further consideration of the caudal dermatoglyphics de- 

 pends upon an appreciation of the functions of the prehensile 

 tail. Carpenter notes in Ateles the use of the tail not only 

 in suspension but also in casting broken-off branches ('35), 

 and the diverse uses of the tail in Alouatta ( '34) are dis- 

 cussed in much greater detail, as follows. 



"The tails of howler monkeys are always in use. During 

 rest and sleep, the tail functions to anchor the animals to 

 the branches of trees. After a young animal is about one 

 month old it uses its tail to secure itself to its mother during 

 rest as well as during locomotion, and this prehensile organ 

 possibly accounts in part for the typical positions in which 

 howler young are carried. The tail is used by resting animals 

 to drive away flies and insects, and apparently as a currying 

 or grooming organ, and I have seen both adult males and 

 females manipulating their genitalia with the tip of the tail. 

 During locomotion, this appendage functions as a grasping 

 organ, and one which counteracts any tendency to fall. . . . 

 The tails of monkeys vary greatly in degree of prehensive- 

 ness, and the howlers rank between capuchin and spider 

 monkeys in this capacity. Capuchin monkeys have a semi- 

 prehensile tail, whereas that of spider monkeys is extremely 

 flexible and adaptive. The degree of prehensiveness is indi- 

 cated by two things: (1) the proportion of the tail which is 

 normally used for grasping, and (2) the arc through which the 

 tail functions, if the point of attachment to the body is taken 

 as a fulcrum about which the tail rotates. The grasping por- 

 tion of howlers' tails roughly corresponds to the part of the 

 tail which has a naked under skin. In an adult, this constitutes 

 20 cm., or about one quarter of the total length of the organ. 

 . . . The prehensile tail is an organ of considerable im- 

 portance in making possible the degree of arborealness found 

 in howling monkeys. ' ' 



Epidermal ridges, just as in the hand and foot, provide 

 for increased security of grasp and heightened sensibility, 

 which would be of service in the various functions indicated 

 above. 



The conditions existing in Alouatta, Ateles and Lagothrix 

 may be regarded as the highest degree of specialization of the 

 caudal skin. Less advanced specialization is to be seen in 



