168 



THE SKELETON. 



upward, the radial side of the base, which has two facets for articulation with the 

 third metacarpal bone, will be on the side to which it belongs. If, as sometimes 

 happens in badly marked bones, one of these facets is indistinguishable, the side 

 may be known by selecting the surface on which the larger articular facet is present. 

 This facet is for 'the fifth metacarpal bone, and would therefore be situated on the 

 ulnar side that is, the one to which the bone does not belong. 



Attachment of Muscles. To three : the Third and Fourth dorsal and Second 

 palmar interosseous. 



The metacarpal bone of the little finger (Fig. 118) presents on its base one facet, 

 which is concavo-convex, and which articulates with the unciform bone, and one 



For third' 



metacarpal. For os 

 magnum 



Fiu. 117. The fourth metacarpul. (Left.) 



For fift h meta- 



carpul 

 For unciform. 



For fourth For cuneiform, 



metacarpal. 



FIG. 118. The fifthjnetacarpal. (Left.) 



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. 



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, Flexor ossis inetacarpi minimi digiti, Fourth dorsal, and Third palmar 

 interosseous. 



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. 



