THE PHALANGES 



167 



sometimes a slip of insertion of the flexor carpi radialis. The shaft of the third metacarpal 

 serves for the origin of the transverse adductor vollicis and two interosseous muscles. The 

 nutrient foramen is directed upward on the radial side and transmits a branch of the second 

 volar metacarpal artery. 



The fourth metacarpal (fig. 201) has a small base. The carpal surface presents two facets: 

 a medial, large and fiat, for articulation with the hamate, and a small facet, at the lateral and 

 posterior angle, for the capitate. On the lateral side are two small oval facets for the correspond- 

 ing surfaces on the third metacarpal and a single concave facet on the medial side for the fifth 

 metacarpal. The shaft of the fourth metacarpal gives attachment to three interosseous muscles, 

 and the nutrient foramen, directed upward on the radial side, transmits a branch of the third 

 volar metacarpal artery. 



The fifth metacarpal (fig. 202) is distinguished by a semilunar facet on the lateral side of 

 the base for the fourth metacarpal, and a rounded tubercle on the medial side for the extensor 

 carpi ulnaris, in place of the usual medial facet. The carpal surface is saddle-shaped for the 

 hamate; the palmar surface is rough for ligaments including the piso-metacarpal prolongation 

 from the flexor carpi ulnaris. The dorsal surface of the shaft presents an oblique line separating 

 a lateral concave portion for the fourth dorsal interosseous muscle from a smooth medial por- 

 tion covered by the extensor tendons of the little finger. The palmar surface gives attachment 

 laterally to the third palmar interosseous muscle and medially to the opponens digiti quinti. The 

 nutrient foramen is directed upward on the radial side and transmits a branch of the fourth 

 volar metacarpal artery. 



THE PHALANGES 



The phalanges (fig. 203) are the bones of the fingers, and number in all fourteen. 

 Each finger consists of three phalanges distinguished as first or proximal, second 



Fir.. 203. — The Phalaxges of the Third Digit of the Haxd. (Dorsal view.) 

 [The arrows indicate the direction of the nutrient canals.) 



Third terminal or ungual phalanx 



Second phalanx 



First phalanx 



or middle, and third or distal. In the thumb, the second phalanx is wanting. 

 Arranged in horizontal rows, the phalanges of each row resemble one another 

 and differ from those of the other two rows. In all the phalanges the nutrient 

 canal is directed downward, toward the distal extremity. 



First phalanx.— The shaft of a phalanx from the first row is flat on the palmar surface, 

 smooth and rounded on the dorsal surface, i. e., semi-cylindrical in shape. The borders of the 

 palmar surface are rough for the attachment of the sheaths of the flexor tendons. The base 

 or metacarpal extremitv presents a single concave articular surface, oval in shape, for the 



