THE SKELETON. 



75 



<sc 



lunar, magnum, second metacarpal, and trapezium. This 

 bone, is not visible on the palmar surface of the wrist. 

 The magnum articulates with the 

 scapholunar, trapezoid, unciform, 

 and second, third, and fourth meta- 

 carpals. The unciform can be recog- 

 nized by its w r edge shape. It articu- 

 lates with the scapholunar, cunei- 

 form, magnum, and fourth and fifth 

 metacarpals. Each carpal bone de- 

 velops from a single center except 

 the scapholunar, which develops 

 from two centers. 



The typical arrangement of the 

 vertebrate carpus is shown in figure 

 36, B. The pisiform does not be- 

 long to the cartilaginous skeleton, 

 butisasesamoidbone. In all mam- 

 mals possessing five digits the an- 

 lage of three bones in the proximal 

 row, five bones in the distal row, 

 and a central element occurs in the 

 embryo, but through fusion of ele- 

 ments a less number is present in 

 most adults. Thus, in the cat the 

 radiale and intermedium and cen- 

 trale unite to form the scapholunar. 

 In all forms carpalia 4 and 5 coal- 

 esce to form the unciform. 



Metacarpus. - There are five 

 metacarpal bones forming the mid- 

 dle region of the forefoot. They 

 are named, beginning on the pollex side, first, second, 

 third, fourth, and fifth metacarpals respectively. Each 



FIG. 37. LATERAL AS- 

 PECT OF LEFT FORE- 

 LIMB OF EQUUS. 



//, Hiimerus; m s , third 

 metacarpal; w 4 , fourth 

 metacarpal; p, phalan- 

 ges; r, radius; s, sesa- 

 moid; sc, scapula; u, 

 ulna; a, scaphoid; c, 

 semilunar; m, cunei- 

 form; n, pisiform; w, 

 magnum; 11, unciform. 



