PHALANGES. 7 01 



forme and the magnum, and by its lateral portions with 

 the third and fifth metacarpal bones. 



The fifth metacarpal bone is smaller and shorter than the 

 fourth. Its carpal extremity presents a double articulating 

 surface, the larger for the unciforme, the smaller for the 

 fourth metacarpal bone. The base presents a tubercle for 

 the insertion of the extensor carpi ulnaris. 



Development. Ossification of the metacarpal bones com- 

 mences by two centres one for the digital extremity, and 

 one for the shaft. About the tenth or twelfth week the 

 metacarpal bone of the thumb presents an exception to this 

 rule, by having its ossific centre in the carpal extremity. 

 The epiphyses show themselves about the second or third 

 year ; and about the twentieth the metacarpal row is com- 

 pleted. 



THE PHALANGES, (Fig. 220.) 



The phalanges compose the bones of the thumb and fin- 

 gers, and have each a shaft and two extremities. 



The thumb has two bones; each of the fingers three, placed 

 in rows. The first row or phalanx is next to the metacar- 

 pal bones. The bones of this row have their base concave 

 for receiving the head of the corresponding metacarpal 

 bone, and, on either side, a small tubercle for the lateral 

 ligament. The lower extremity presents two small heads, 

 or a pulley-like formation, for articulating with the second 

 phalanx ; the sides form ridges for the thecal attachments. 

 The dorsal surface is convex and smooth, the palmar 

 concave. 



The second phalanx is smaller than the first; its superior 

 extremity presents two small cavities for the two heads of 

 the first phalanx ; the lower extremity is slightly concave 

 for articulation with the third phalanx. 



The third or last phalanx is the smallest of the three, 

 and is remarkable for having its lower extremity flat, thin, 

 and semicircular, and its palmar surface rough. The first 

 phalanx of the thumb is stronger and shorter than those 

 of the fingers, while its second or last phalanx is broader. 



