Abstract
The second or index finger of the slow loris(Nycticebus coucang javanicus)is unusually shorter than the other fingers, indicating that it may not be involved in grasping function. In addition, the second digit of the foot of slow loris has a hooked claw or comb nail, in contrast to flat claws of the other digits on the foot. These morphological specification of the index finger suggest a corresponding functional difference. All digits have round soft pads on their tip of palmar side. Together with well developed metacarpal and metatarsal pads, the thumb and the third, fourth and fifth digits constitute main structure for grasping. In humans, for example, the index finger is not used to grasp the grip of a tennis racquet or golf club. Thus this specialization of the index finger implies that a different function is being served. The specialization is more prominent in potto(Perodicticus potto). Other families such as the galago, marmoset, tarsiers, and lemur, do not show a comparable specialization of the index finger. Thus the slow loris is a good model for the investigation of genes involved in second finger differentiation, as well as of those involved in transformation of hook to flat nail.
