204 



SPECIAL ANATOMY OF THE SKELETON 



unciform bone, and one lateral, articular facet, which articulates with the fourth 

 metacarpal bone. On its ulnar side is a prominent tubercle, for the insertion of 

 the tendon of the Extensor carpi ulnaris. The dorsal surface of the shaft is marked 

 by an oblique ridge which extends from near the ulnar side of the upper extremity 

 to the radial side of the lower. The outer division of this surface serves for 

 the attachment of the Fourth dorsal interosseous muscle; the inner division is 

 smooth and covered by the Extensor tendons of the little finger. 



For 



metacarpal. For os 

 magnum. 



For fifth meta- 

 carpal 

 For unciform. 



For fourth 

 metacarpal. 



FIG. 164. The fourth metacarpal. (Left.) 



For unciform. 

 FIG. 165. The fifth metacarpal. (Left.) 



If this bone is placed with its base toward the student and its palmar surface upward, the 

 side of the head which has a lateral facet will be that to which the bone belongs. 



Attachment of Muscles. To five the Extensor carpi ulnaris, Flexor carpi ulnaris, Oppo- 

 nens minimi digiti, Fourth dorsal, and Third palmar interossei. 



Articulations. Besides the phalangeal articulations, the first metacarpal bone articulates 

 with the trapezium; the second with the trapezium, trapezoid, os magnum, and third metacarpal 

 bones; the third with the os magnum and second and fourth metacarpal bones; the fourth with 

 the os magnum, unciform, and third and fifth metacarpal bones; and the fifth with the unciform 

 and fourth metacarpal. 



The first has no lateral facets on its carpal extremity; the second has no lateral facet on its 

 radial side, but one on its ulnar side; the third has one on its radial and two on its ulnar side; 

 the fourth has two on its radial and one on its ulnar side; and the fifth has only one on its radial 

 side. 



The Phalanges of the Hand (Phalanges Digitorum Manus). 



The phalanges (internodia; phalanges digitorurn manus) are fourteen in num- 

 ber, three for each finger, and two for the thumb. In numbering them the 

 proximal bone is designated as the first phalanx (phalanx /). They are long 

 bones, and present for examination a shaft and two extremities. The shaft 

 (corpus phalangis) tapers from above downward, is convex posteriorly, concave 

 in front from above downward, flat from side to side, and marked laterally by 

 rough ridges, which give attachment to the fibrous sheaths of the Flexor tendons. 

 A nutrient foramen on the palmar surface leads into a nutrient canal which runs 

 toward the periphery (distad). The metacarpal extremity, or base (basis phalangis), 

 of each phalanx in the first row presents an oval, concave, articular surface, 

 broader from side to side than from before backward; and the same extremity 



