METACARPUS. 699 



cave to join the scaphoid ; below it unites with the second 

 metacarpal bone, and internally with the os magnum. 



The os magnum, so named from fts size, is situated upon 

 the ulnar side of the last, and is the largest of the bones of 

 the carpus. Its superior surface articulates with the sca- 

 phoid and lunar bones ; its inferior, with the second, third, 

 and fourth metacarpal. Internally it meets the unciform, 

 externally the trapezoides. The dorsal surface is broad, 

 the palmar narrow. 



The os unciforme, so named from its hook-like process, is 

 the next in size to the os magnum. Its superior surface 

 joins the os-lunare, its external the magnum, its internal 

 the cuneiform, and its base the fourth and fifth metacarpal. 

 Its dorsal surface is rough ; and its palmar presents the 

 hook-like process for the attachment of "'the annular liga- 

 ment. 



Structure. The bones of the carpus consist of cellular 

 structure, covered by a delicate lamina of compact bone. 

 They are developed from a single point of ossification, 

 except thounciform, which has two. 



Ossification is observed to begin in the os magnum and 

 unciforme, at the close of the first year ; in the cuneiform, 

 at the close of the third; in the trapezium and semilunare, 

 in the fifth ; in the scaphoid^ from the sixth to the eighth; 

 in the trapezoides, from the eighth to the ninth, and in the 

 pisiforme in the twelfth year. 



THE METACARPUS, (Fig. 220.) 



The metacarpus is situated between the carpus and 

 the phalanges, and consists of five bones. Those corre- 

 sponding to the fingers are parallel to each other ; the 

 one for the thumb' stands out from the rest at an angle. 

 Each metacarpus is composed of a head, shaft and base. 

 The head is at the digital extremity, and articulates with 

 the first phalanx of the fingers ; the shaft is triangular, 

 and marked laterally for the attachment of the interossei 

 muscles ; the base is superior, and articulates with its fel- 

 lows and with the carpal bones. 



