80 



THE OSTEOLOGY AND MYOLOGY 



convexity for the radius and scaphoid respectively, and one upon its concavity for the spur 

 of the unciform ; its distal border touches the magnum ; its proximal border the cuneiform. 

 It is thus in relation with five bones, as in the human hand. The cuneiform is wedged 

 between the ulna, semilunar, unciform and pisiform ; its ulnar f\icet is large and concave ; 

 that for the unciform next largest and concavo-convex ; that for the pisiform plane, and 

 continuous with the ulnar one. It merely touches the semilunar. The ^jisj/brm is the 

 largest bone of this row, having a produced and knobbed free extremity, and looking, in 

 fact, like an aborted metacarpal. Of its two facets, the large flat one is for the cuneiform ; 

 the smaller concave one combines with a similar one on the cuneiform to make a depres- 

 sion for the ulna. Its knob aftbrds attachment and leverage to the flexor carjn ulnaris,a.nA. 

 some muscles proper to the hand. The trapezium is very small, and irregularly triangular ; 

 it bears an oval depression for the head of the first metacarpal, a plano-concave facet for 

 the trapezoid, and a little smooth surface for the distal sesamoid. It is scarcely to be called 

 properly articulated with the scaphoid. The trcqjezoid is still smaller; its metacarpal facet 

 only receives part of the head of the second metacarpal, which reaches the trapezium on one 

 side, and the os magnum, on the other ; the bone articulates with the magnum, trapezium and 

 scaphoid, but is excluded by the pointed process of the latter from the semilunar. The Tnag- 

 num is larger than either of the last two, but nevertheless smaller than the unciform ; the 

 metacarpal fticet is divided by a sharp, vertical ridge into two parts, one supporting part of 

 the head of the second metacarpal, and the other the whole of the head of the third meta- 

 carpal. The bone has an elongated facet for the unciform, a small convexity for the semi- 

 lunar, and an irregular surfiice for the trapezoid ; it also appears to touch the process of the 

 scaphoid, and the side of the head of the fourth metacarpal. The unciform is the largest 

 bone of the wrist, and supports the two outer metacarpals upon one facet, divided by a 

 barely appreciable ridge ; it is singularly irregular in contour, having a large hooked process 

 that curves under the base of the fifth metacarpal, and a similar, but smaller and straighter 

 prolongation between the cuneiform and magnum. 



Tliese ten bones together form a much arched wrist, concave in front from side to side, 

 and correspondingly convex across the anconal aspect. The deep groove along the pal- 

 mar surface is filled by the flexor tendons. The bones are very closely packed and inter- 

 locked ; almost the only irregularity of superficies is that caused by the knob of the 



pisiform and hook of the unciform. The composition of 

 the wrist is strikingly like that of man ; the two sesa- 

 moids aside, there is really little difference to be noted, 

 although none of the bones have precisely the same shape 

 and mutual relation. The sinking of the ulna into the 

 depression common to the cuneiform and pisiform, the 

 exclusion of the trapezoid from contact with the semilu- 

 nar, and the size and shape of the unciform and pisiform 

 are among the chief differences displayed. The unciform 

 and magnum appear to change places as regards the extent of metacarpal support they fur- 

 nish, the former having here the largest articulating surface. 



Metacarpus. — The five metacarpals are all of different lengths — the middle one being the 

 longest, the second and fourth successively a little shorter, and the fifth much less than the 

 fourth, which only slightly exceeds the first — the latter being the shortest. The four 



Fig. 23. 

 Heads of Metacarpals enlarged. 



