2o6 A MANUAL OF ANATOMY 



three facets. The middle one is the largest, and articulates with 

 the third metacarpal bone. The external one is a narrow, concave 

 strip for the second metacarpal bone. The internal one, small 



For 3rd Metacarpal 



For Scaphoid 



Head (for Semilunar 



For Trapezoid For Unciform 



— For 2nd Metacarpal 



For Unciform ^ 



B 



For 4th Metacarpal 



Fig. 119. — The Right Os Magnum. 

 A, External Vrew ; B, Internal View. 



and circular, tips inferiorly the projecting postero-internal angle, 

 and articulates with the fourth metacarpal bone. 



Articulations. — Superiorly with the semilunar, superiorly and 

 externally with the scaphoid, inferiorly with the second, third, and 

 fourth metacarpal bones, externally with the trapezoid, and internally 

 with the unciform. 



The Unciform Bone. 



The unciform bone is characterized by a hook-like process on its 

 palmar surface. It is triangular, or wedge-shaped, and lies with its 

 base downwards. The superior extremity presents a narrow facet 

 for the semilunar. The inferior surface is divided by an antero- 

 posterior ridge into two quadrilateral facets, the outer of which 

 articulates with the fourth, and the inner with the fifth, meta- 

 carpal bone. The palmar surface, which is rough, presents at its 

 lower and inner part a prominent curved projection, called the unci- 

 form process. This process is laterally compressed, the external 

 surface being concave and the internal convex, so that the direction 

 of the curve is outwards. Its borders are superior, inferior, and 

 anterior. The internal surface gives origin to the flexor brevis, and 

 opponens, minimi digiti, and close to the root it presents the ulnar 

 groove for the deep branches of the ulnar artery and nerve. The 

 anterior border gives attachment to the anterior annular and pisi- 

 uncinate ligaments. The dorsal surface is extensive and rough. 

 The external surface presents an elongated facet, broad above .and 

 narrow below, where it is confined to the back part, for articula- 

 tion with the OS magnum. The supero-internal surface is con- 

 cavo-convex from below upwards, and articulates with the cuneiform. 

 The internal border, situated at the meeting of the supero-internal 

 and inferior surfaces, is narrow and rough, its direction being from 

 before backwards. 



