CARPUS. 223 



pezium. This surface gives attachment to the Abductor Pollicis, Flexor Ossis 

 Metacarpi, and Flexor Brevis Pollicis muscles ; and the anterior annular liga- 

 ment. The posterior or dorsal surface is rough, and the external surface also 

 broad and rough, for the attachment of ligaments. The internal surface presents 

 two articular facets: the upper one, large and concave, articulates with the 

 trapezoid ; the lower one, narrow and flattened, with the base of the second 

 metacarpal bone. 



To ascertain to which hand it belongs, hold the bone with the grooved 

 palmar surface upwards, and the external broad, nonarticular surface back- 

 wards ; the saddle-shaped surface will then be directed to the side to which the 

 bone belongs. 



Articulations. With four bones: the scaphoid above, the trapezoid and 

 second metacarpal bones internally, the first metacarpal below. 



Attachment of Muscles. Abductor Pollicis, Flexor Ossis Metacarpi, and part 

 of the Flexor Brevis Pollicis. 



The Trapezoid is the smallest bone in the second row. It may be known by 

 its wedge-shaped form, the broad end of the wedge forming the dorsal, the nar- 

 row end the palmar surface ; and by its having four articular surfaces touching 

 each other, and separated by sharp edges. The superior surface, quadrilateral 

 in form, smooth and slightly concave, articulates with the scaphoid. The infe- 

 rior surface articulates with the upper end of the second metacarpal bone ; it is 

 convex from side to side, concave from before backwards, and subdivided, by 

 an elevated ridge, into two unequal lateral facets. The posterior or dorsal and 

 anterior or palmar surfaces are rough, for the attachment of ligaments, the 

 former being the larger of the two. The external surface, convex and smooth, 

 articulates with the trapezium. The internal surface is concave and smooth 

 below, for articulation with the os magnum ; rough above, for the attachment 

 of an interosseous ligament. 



To ascertain to which side this bone belongs, let the broad dorsal surface be 

 held upwards, and the inferior concavo-convex surface forwards; the internal 

 concave surface will then point to the side to which the bone belongs. 



Articulations. With four bones: the scaphoid above, second metacarpal bone 

 below, trapezium externally, os magnum internally. 



Attachment of Muscles. Part of the Flexor Brevis Pollicis. 



The Os Magnum is the largest bone of the carpus, and occupies the centre of 

 the wrist. It presents above a rounded portion or head, which is received into 

 the concavity formed by the scaphoid and serailunar bones ; a constricted por- 

 tion or neck; and, below, the body. The superior surface is rounded, smooth, 

 and articulates with the semilunar. The inferior surface is divided by two 

 ridges into three facets, for articulation with the second, third, and fourth meta- 

 carpal bones ; that for the third (the middle facet) being the largest of the three. 

 The posterior or dorsal surface is broad and rough; the anterior or palmar, nar- 

 row, rounded, and also rough, for the attachment of ligaments. 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. 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 sur- 

 face articulates with the unciform by a smooth, concave, oblong facet, which 

 occupies its posterior and superior parts; and is rough in front, for the attach- 

 ment of an interosseous ligament. 



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

 held upwards, and the broad dorsal surface forwards; the internal soncave 

 articular surface will point to its appropriate side. 



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. 



