The Skeleton of the Posterior Limb. 165 



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. 



THE METACARPUS AND PHALANGES. 



The metacarpus (Fig. 68) 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. 



SESAMOID BONES. 



Accessory elements, sesamoid bones (ossa sesamoidea) 

 developed in connection with the ligaments of muscles, are found 

 on the volar surface of the foot in association with certain of the 

 joints. They occur in transverse pairs at the metacarpophalangeal 

 articulations and in linear pairs at the articulations of the second 

 with the third phalanges. The pisiform bone of the carpus is also 

 a sesamoid, being formed in the insertion tendon of the flexor carpi 

 ulnaris muscle. 



THE SKELETON OF THE POSTERIOR LIMB. 



In the posterior limb the proximal or girdle portion comprises 

 the paired COXal bones, which are united ventrally at the pelvic 

 symphysis, thus forming the pelvic girdle. The distal portion — ■ 

 comprising, as in the anterior limb, the supports of the free ex- 



