THE CARPUS 197 



ment to the anterior annular ligament of the wrist and sometimes a few fibres 

 of the Abductor pollicis. The external surface is rough and narrow, and gives 

 attachment to the external lateral ligament of the wrist. The internal surface 

 presents two articular facets; of these, the superior or smaller one is flattened, 

 of semilunar form, and articulates with the semilunar; the inferior or larger is 

 concave, forming, with the semilunar bone, a concavity for the head of the os 

 magnum. 



To ascertain to which side the bone belongs, hold the convex radial articular surface upward, 

 and the dorsal surface backward; the prominent tubercle will be directed to the side to which 

 the bone belongs. 



Articulations. With five bones the radius above, trapezium and trapezoid below, os 

 magnum and semilunar internally. 



Attachment of Muscles. Occasionally a few fibres of the Abductor pollicis. 



The semilunar bone (Fig. 154) may be distinguished by its deep concavity and 

 crescentic outline. It is situated in the centre of the upper row of the carpus, 

 between the scaphoid and cuneiform. 



For cuneiform. For radius 



For scaphoid 

 For unciform For os magnum 



A B 



FIG. 154. The left semilunar. A, anterior and internal surfaces; B, external surface. 



Surfaces. The superior surface, convex, smooth, and bounded by four edges, 

 articulates with the radius. The inferior surface is deeply concave, and of greater 

 extent from before backward than transversely; it articulates with the head of the 

 os magnum and by a long, narrow facet (separated by a ridge from the general 

 surface) with the unciform bone. The anterior or palmar and posterior or dorsal 

 surfaces are rough, for the attachment of ligaments, the former being the broader 

 and of a somewhat rounded form. The external surface presents a narrow, flat- 

 tened, semilunar facet for articulation with the scaphoid. The internal surface 

 is marked by a smooth, quadrilateral facet, for articulation with the cuneiform. 



To ascertain to which hand this bone belongs, hold it with the dorsal surface upward, and 

 the convex articular surface backward; the quadrilateral articular facet will then point to the 

 side to which the bone belongs. 



Articulations. With five bones the radius above, os magnum and unciform below, scaphoid 

 externally, and cuneiform internally. 



The cuneiform (os triquetrum) (Fig. 155) may be For pisiform For semilunar 

 distinguished by its pyramidal shape, and by its 

 having an oval, isolated facet for articulation with the 

 pisiform bone. It is situated at the upper and inner 

 .side of the carpus. 



Surfaces. The superior surface presents an internal, For unciform 



vough, nonarticular portion, and an external or FIG 155 The left cuneiform, 

 articular portion, which is convex, smooth, and articu- % ne palmar and later 

 lates with the triangular intra-articular fibrocartilage 



of the wrist. The inferior surface, directed outward, is concave, sinuously curved, 

 and smooth for articulation with the unciform. The posterior or dorsal surface is 



