34 MR. R. I. POCOCK ON THE EXTERNAL 



remarkable particulars from that of the other genera hitherto 

 noticed. It is capable of being turned at right angles to the axis 

 of the forearm. Tlie pahn is short and broad, and the powerful 

 pollex can be set so far backwards that its long axis is practically 

 in the same line as that of the palm aiid of the fourth and 

 longest digit, thus giving the widest possible span to the extre- 

 niit}^ and when the pollex is in this position the internal proximal 

 pad, constituting the proximal portion of the "ball" of the 

 thumb, lies nearly in a line behind the external proximal pad. 

 Tlie pollex, moreover, is incomparably more strongly opposable 

 than in any other genus of Lemuroid Primates, and surpasses 

 even the thumb of Man in that respect. When brought into 

 opposition, the composite ball of the thumb is pressed against the 

 second intermediate pad and the external proximal pad. Except 

 that the hallux is a little longer and stronger than the pollex, 

 the feet conform to the hands in type. In all other genera of 

 Primates the two extremities are dissimilar. 



As is well known, the second digit of the hand in Nycticebus is 

 dwarfed and in Perodicticus is represented by an excrescence 

 upon the second intermediate pad. For the rest the hand of 

 Perodicticus is narrower with reference to its span, and the third 

 and fifth digits are tied basally by a shallow web to the fourth, 

 so that the three cannot be so widely separated as in A^i/ciicebus. 

 In the feet of both genera the heel is hair}^ and shorter than the 

 naked part of the sole, the second digit is dwarfed, and the third 

 and fifth are basally webbed to the foui'th in Perodicticus, free 

 in Nycticehus, The nails on both extremities are larger in the 

 former than in the latter genus (text-fig. 8, A, B, C, D). 



The published descriptions of the extremities of Arctocehus 

 suggest that they differ from those of Perodicticus in having the 

 third, fourth, and fifth digits more completely webbed (see P. Z. S. 

 1864, pp. 316-317, 319-320). Huxley, however, states that the 

 calcaneal tuberosity of the foot is naked and separated from the 

 padded portion by a narrow band of hair. But since the heel is 

 without exception covered with hair in all the remaining species 

 of arboreal * lemuroid Primates, I suspect that the nakedness 

 mentioned by Huxley was due to artificial rubbing in the specimen 

 he examined. It is not uncommon for the hair to be worn 

 o(i' the heels in captive examples of common lemurs (Z. albifrons, 

 etc.). 



In the distinctness and separation of the pads and their 

 encircling ai-r.angement round a cential palmar ai-ea,, the hand of 

 Tarsius recalls that of Hemiyalago ; but there are certain differ- 

 ences. The hand and fingers of Tarsius are relatively longer, 

 the pollex is smaller, closer to the second digit and not opposable, 

 the third digit is the longest of the series, slightly surpassing the 

 second and fourtli, which are subequal. The first, or pollical, 



* Lemiir criffa, winch lias the heels iiaked alone: the middle line, lives in 

 rocky hills. 



