166 



THE SKELETON 



The base presents a saddle-shaped articular surface for the greater multangular, prolonged in 

 front into a thin process. There are no lateral facets, but laterally a small tubercle receives 

 the insertion of the abductor pollicis longus. Medially is a rough area from which fibres of the 

 inner head of the flexor pollicis brevis take origin. The margin of the articular surface gives 

 attachment to the articular capsule of the carpo-metacarpal joint. The inferior extremity or 

 head is rounded and articular, for the base of the first phalanx; the greatest diameter is from 

 side to side and the surface is less convex than the corresponding surface of the other metacarpal 

 bones. On the volar surface it presents two articular eminences corresponding to the two 

 sesamoid bones of the thumb. Of the two margins, the medial gives origin to the lateral 

 head of the^rs^ dorsal interosseous, the lateral receives fibres of insertion of the opponens pollicis. 



Fig. 201. — The Fourth (Left) Metacarpal. 



Radial side 



For third metacarpal | 

 For capitate 



Ulnar side 



For fifth metacarpal 



The second metacarpal (fig. 199). — The distinctive features of the four remaining meta- 

 carpals are almost exclusively confined to the carpal extremities. The second is easily recog- 

 nised by its deeply cleft base. The terminal surface presents three articular facets, arranged 

 as follows, from lateral to medial border : — (1) a small oval facet for the greater multangular; (2) 

 a hollow for the lesser multangular; and (3) an elongated ridge for the capitate. The dorsal 

 surface is rough for the insertions of the extensor carpi radialis longus and a part of the extensor 

 carpi radialis brevis; the palmar surface receives the insertion of the flexor carpi radialis and 

 gives origin to a few fibres of the oblique adductor pollicis. The lateral aspect of the extremity 

 is rough and non-articular; the medial surface bears a bilobed facet for the third metacarpal. 



Fig. 202. — The Fifth (Left) Metacarpal. 



Radial side 



Fourth metacarpal 



Ulnar side 



The shaft of the sccf)nd metacarpal gives attachment to three interosseous muscles, and the 

 nutrient foramen, directed upward on the ulnar .side, transmits a branch of the second volar 

 metacarpal artery. 



The third metacarpal (fig. 200) is distinguished by the prominent styloid process projecting 

 upward fr(ttu the lateral and jjo.stcrior angle of the base. Immediately below it, on the dorsal 

 surface, is a rough iiuprfssioii for the extensor carpi radialis brevis. The carpal surface is 

 concave behind and convex in front, and articulates with the middle of the three facets on the 

 inferior surface of the cajjitate. On the lateral side is a bilobed articular facet for the second 

 metacarpal, and on the medial .side two small oval facets for the fourth metacarpal. The volar 

 a.spect of the ba.se is rough and gives attachtneiit to fibres of the oblique adductor pollicis and 



