650 MAMMALIAN ANATOMY 



hand; the remaining four digits, as usual, are normal. I have col- 

 lected several examples of this type of variation. 



3. The hand has seven digits, whereof the first is always in- 

 different, and either rudimentary or with two or three phalanges. 

 The second and third digits are usually more or less united ; the 

 second is always formed like a digit of the opposite hand ; the third 

 is always indifferent, and varies in development from a small nail to a 

 complete digit with its own metacarpal. The remaining four digits 

 are normal (Fig. 51lA). 



In polydactylous hands the carpal bones are often abnormal ; the 

 scapho-lunar is always very wide, and may be united with the trape- 

 zium ; the trapezoid may be greatly enlarged, or there may be two 

 trapezoids and a separate trapezium. 



HUMAN HAND. 



The human Carpus has one more bone than the carpus of the cat ; 

 the scaphoid and the semilunar are not united. The pisiform is a 

 rounded and relatively small bone ; the trapezoid resembles in shape 

 the trapezium of the cat; the magnum is larger and more regular, 

 and the unciform exhibits a strong palmar hook. 



The scaphoid (Fig. 512, 1) articulates by an oval proximal con- 

 vexity (b) with the radius, by a distal concavity (c) with the magnum, 

 by a crescentic facet on the ulnar margin (d) with the semilunar, and 

 by a triangular area at the radial end of the dorsal surface (e) with 

 the trapezium and the trapezoid. It presents on the dorsal surface 

 (Fig. 513) a transverse ridge for ligaments, and at the radial palmar 

 end a well-marked tubercle. 



The semilunar (Fig. 512, 2) is obliquely crescent-shaped; the con- 

 cave surface is distal (b) and articulates with the magnum, except 

 along a small ulnar strip (c) which joins the unciform. The ulnar 

 surface is flattened and exhibits an oval area (d) for articulation with 

 the cuneiform. The convex proximal surface (a} moves upon the 

 radius. The crescentic radial surface articulates with the scaphoid. 



The cuneiform (Fig. 512, 3) is pyramidal. Its radial surface (b) 

 articulates with the semilunar. Its distal surface is occupied by a large 

 undulating facet (c) for the unciform. The ulnar half of the palmar 

 surface bears a circular, slightly convex facet (d) for the pisiform. 



The pisiform (Fig. 512, 4) is an oval bone, the long axis of which 



