THE BONES OF THE ANTERIOR LIMB 205 



with the radius and ulna; and a distal row, the elements of which 

 are articulated with the five bones of the metacarpus. Enumerated 

 from the medial side of the wrist laterad, the proximal row contains 

 four elements, namely, the navicular, lunate, triquetral, and pisi- 

 form bones. The navicular and lunate are the radiale and inter- 

 medium of the primary terrestrial limb skeleton (p. 03) and are articu- 

 lated with the distal extremity of the radius. The triquetral is the 

 ulnare of the basic pattern and is articulated with the styloid 

 process of the ulna. The pisiform bone lies on the ventral surface 

 of the extremity of the ulna, and is therefore not exposed to the 

 dorsal surface of the wrist. It is really a sesamoid bone (p. 206) 

 added to the primary three proximal carpals. The distal row 

 contains five elements, namely, the greater multangular, lesser 

 multangular, central, capitate, and hamate bones. The first, 

 second, and fourth are in association respectively with the first, 

 second, and third metacarpals. The central bone lies to the lateral 

 side of the articulation at the base of the second metacarpal. 

 As its name implies, it is originally an element interposed between 

 the proximal and distal rows. The hamate is a comparatively 

 large element associated with the fourth and fifth metacarpals, but 

 extending also to the articulation of the third, where it tends to 

 replace the greatly reduced capitate. It represents the two lateral 

 members of the original distal row of carpals (Fig. 36) fused together. 



The Metacarpus and Phalanges 



The metacarpus (Fig. 94) comprises five stout elements, the 

 metacarpal bones (ossa metacarpalia), which form the basal 

 supports of the digits. Each consists, in addition to a main 

 portion or body, of a flattened proximal end, or base, and a rounded 

 distal extremity, or head. The four lateral bones are normally 

 developed, while the first, which belongs to a reduced digit, is of 

 very small size. 



The phalanges, or bones of the digits, are distributed according 

 to the formula 2, 3, 3, 3, 3. They are similar in form to the meta- 

 carpals, with the exception, however, of the terminal, ungual 

 phalanges, which are laterally compressed, pointed, and cleft at 

 their tips for the attachment of the claws. 



