6o 



ELEMENTS OF MAMMALIAN ANATOMY. 



The typical arrangement of the vertebrate carpus is 

 shown in figure 36, B. The pisiform does not belong to the 

 cartilaginous skeleton, but is a sesa- 

 moid bone. In all mammals pos- 

 ** $\ sessing five digits, the anlage 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 elements a 

 less number is present in most adults. 

 Thus, in the cat the radiale and in- 

 termedium and centrale unite to form 

 the scapholunar. In all forms car- 

 palia 4 and 5 coalesce to form the 

 unciform. 



Metacarpus. There are five 

 metacarpal bones forming the middle 

 region of the forefoot. They are 

 named, beginning on the pollex side, 

 first, second, third, fourth, and fifth 

 metacarpals respectively. Each bone 

 consists of a proximal extremity or 

 base, a middle portion or shaft, and 

 a distal extremity or head (Fig. 

 36). These bones are curved so as 

 to be slightly convex on the dorsal 

 aspect. 



The number of metacarpals in 

 mammals varies from one in Equus 

 to five which are present in most 

 orders. Nearly all the species of every 

 order, except the Edentata and Un- 



gulata, possess five metacarpals. In the pig and hippopota- 

 mus there are four metacarpals, in the rhinoceros three, and 



FIG. 37. LATERAL AS- 

 PECT OF LEFT FORE- 

 LIMB OF EQUUS. 



h, Humerus ; m$, third 

 metacarpal ; mi, fourth 

 metacarpal ; p, phalan- 

 ges ; r, radius ; s, sesa- 

 moid; sc, scapula; ua, 

 ulna; a, scaphoid; c, 

 semilunar ; m, cunei- 

 form ; n, pisiform; w, 

 magnum; u, unciform. 



