200 SPECIAL ANATOMY OF THE SKELETON 



middle facet) being the largest of the three. The posterior or dorsal surface is 

 broad and rough; the anterior or palmar, narrow, rounded, and also rough, for the 

 attachment of ligaments, and it gives origin to a part of the Adductor obliquus 

 pollicis and to the deep head of the Flexor brevis pollicis. The external surface 

 articulates with the trapezoid by a small facet at its anterior inferior angle, behind 

 which is a rough depression for the attachment of an interosseous ligament. 



x^VfV'^5\. * For semilunar 



For 2nd metacarpal ^ 



metacarpal For 4th metacarpal Palmar surfac 



A B 



FIG. 159. The left os magnum. A, outer side seen from below; B, internal posterior surface. 



Above this is a deep and rough groove, which forms part of the neck and serves 

 for the attachment of ligaments, bounded superiorly by a smooth, convex surface 

 for articulation with the scaphoid. The internal surface articulates with the 

 unciform by a smooth, concave, oblong facet which occupies its posterior and 

 superior parts, and is rough in front, for the attachment of an interosseous 

 ligament. 



To ascertain to which hand this bone belongs, the rounded head should be held upward, and 

 the broad dorsal surface forward; the internal concave articular surface will point to the side to 

 which the bone belongs. 



Articulations. With seven bones the scaphoid and semilunar above; the second, third, and 

 fourth metacarpal below; the trapezoid on the radial side; and the unciform on the ulnar side. 



Attachment of Muscles. Part of the Adductor obliquus pollicis and the deep head of the 

 Flexor brevis pollicis. 



The unciform (os hamatum) (Fig. 160) may be readily distinguished by its 

 wedge-shaped form and the hook-like process that projects from its palmar surface. 

 It is situated at the inner and lower angle of the carpus, with its base downward, 

 resting on the two inner metacarpal bones, and its apex directed upward and 

 outward. 



For semilunar 



For os magnum 

 For cuneiform 



For 4th metacarpal 



For 5th metacarpal Unciform process For 5th metacarpal 



A B 



FIG. 160. The left unciform. A, internal surface; B, outer and distal surfaces. 



Surfaces. The superior surface, the apex of the wedge, is narrow, convex, 

 smooth, and articulates with the semilunar. The inferior surface articulates with 

 the fourth and fifth metacarpal bones, the concave surface for each being sepa- 

 rated by a ridge which runs from before backward. The posterior or dorsal 



