GREGORY: NOTHARCTUS, AN AMERICAN EOCENE PRIMATE 



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ton the stout pollex (I) diverges widely from the elongate digits III and IV; the slender digit II is often 

 placed midway between I and III; III and IV are close together, IV being the longest and heaviest and 

 V shorter than III. The carpus is narrow proximally and wide distally; the scaphoid is wide, the lunar 

 very narrow and small, the trapezium large, the magnum narrow and extended vertically; the unciform 

 is large and even more extended vertically. The wide shallow centrale lies between the unciform, mag- 

 num and trapezoid below and the lunar and scaphoid above; it has contact with the unciform, a special- 

 ization which may be correlated with the extreme divergence of the pollex and the crowding of the carpal 

 elements toward the ulnar side. The metacarpal of digit I is stout and short; metacarpals II-V are 

 slender, II being considerabty shorter than III, which is a little longer than IV. The proximal phalanges 

 are stout and long, the middle row in digits II-V stout; the distal row are very short and bear flattened, 

 crescentic expansions for the flat nails and for the expanded finger tips below. 



In many of these characters Lemur parallels the opossums: e. g., in the fan-like arrangement of the 

 digits, in the divergent pollex, in the small size of the lunar, in the widening ol the distal row of the carpals, 

 in the vertical extension of the magnum and of the unciform, in the elongation of the fourth digit and 

 in its association Avith the third, etc. 



Huxley, Dollo, Anthony and others have shown how such features in the opossum render the manus 

 of that animal especially effective in firmly grasping the branches of trees. The primitive primates 

 exhibit similar characters and also have the advantage of expanded finger tips and greatly expanded pads 

 on the palm of the hand. 



In Cebus these presumably primary adaptations, or palffiotelic characters, have been partly obscured 

 by several adaptations and functions which are probably ctenotelic. First, pari passu with the increas- 

 ing versatility which is expressed in the larger brain and in the form of the humerus, the manus has per- 

 haps become better adapted for running lightly along the surface of the branches, as shown in the more 

 symmetrical development of the digits on either side of digit III and possibly in the shortening of the 

 digits. Secondly, the mode of progression which has been designated as "brachiation," and which con- 

 sists in swinging the body from branch to branch partly by means of the forearms, the hands l)eing held 

 above the head, the palms facing each other and the digits well flexed, has been adopted in moderate 

 degree by Cehus, and is perhaps indicated by the widening of the carpus, b^ the more symmetrical arrange-, 

 ment of the digits on either side of digit III, by the less divergence and greater mobility of the pollex, 

 by the globular expansion of the distal ends of the metacarpals, and by the narrowing of the distal 

 phalanges, the claws being bent up almost into nails. In correlation with the lessened divergence of 

 the pollex there has been a readjustment of the carpals so that the lunar is widened and the magnum 

 separates the centrale from contact with the unciform. 



All these readjustments result in the transformation of the manus from a mere grasping organ, used 

 chiefly for clinging to the branches, into a true hand, provided with a more or less opposable thumb and 

 capable of delicately coordinated motions. The dexterity of a cebid monkey in the use of its hands is 

 well illustrated in the following incident related by Thomas Belt in his "Naturalist in Nicaragua." 



' Mickey's ' actifins were yvry liuman-like. Wlien anvfine came near to fondle liim, he ne\ er neglected the opportunity 

 of pocket-picking. He would pull out letters, and quickly take them from their en\ elopes. Once he abstracted a small 

 bottle of turpentine from the pocket of our medical officer. He drew the cork, held it first to one nostril then to the 

 other, made a wry face, recorked it, and returned it to the doctor. 



The exercise of this function is especially facilitated by the globular foi'm of the heads, or distal facets, 

 of the metacarpals and by the drawing in of the pollex toward the remaining digits. 



