CARPUS. 145 



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

 held upwards, and its 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 semilunar bones ; a constricted portion 

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

 articulates with the semilunar. Its inferior surface is divided by two ridges into 

 three facets, for articulation with the second, third, and fourth metacarpal bones ; 

 that for the third, the middle facet, being the largest of the three. The posterior 

 or dorsal surface is broad and rough ; and the anterior or palmar, narrow, rounded, 

 but 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 surface articulates with the unciform 

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

 parts ; rough in front, for the attachment 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 concave 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. 



Attachment of Muscles. Part of the Flexor brevis pollicis. 



The Unciform bone 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 downwards, resting on the two 

 inner metacarpal bones, and its apex directed upwards and outwards. Its superior 

 surface, the apex of the wedge, is narrow, convex, smooth, and articulates with 

 the semilunar. Its inferior surface articulates with the fourth and fifth meta- 

 carpal bones, the concave surface for each being separated by a ridge, which runs 

 from before backwards. The posterior or dorsal surface is triangular and rough, 

 for ligamentous attachment. The anterior or palmar surface presents, at its lower 

 and inner side, a curved, hook-like process of bone, the unciform process, directed 

 from the palmar surface forwards and outwards. It gives attachment, by its 

 apex, to the annular ligament ; by its inner surface, to the Flexor brevis minimi 

 digiti, and the Flexor ossis metacarpi minimi digiti ; and is grooved on its outer 

 side, for the passage of the Flexor tendons into the palm of the hand. This is one 

 of the four eminences on the front of the carpus, to which the anterior annular 

 ligament is attached ; the others being the pisiform internally, the oblique ridge 

 of the trapezium, and the tuberosity of the scaphoid externally. The internal 

 surface articulates with the cuneiform by an oblong surface, cut obliquely from 

 above downwards and inwards. Its external surf ace articulates with the os mag- 

 num by its upper and posterior part, the remaining portion being rough, for the 

 attachment of ligaments. 



To ascertain to which hand it belongs, hold the apex of the bone upward^ and 

 the broad dorsal surface backwards ; the concavity of the unciform process will 

 be directed to the side to which the bone belongs. 



Articulations. With five bones : the semilunar above, the fourth and fifth meta- 

 carpal below, the cuneiform internally, the os magnum externally. 



Attachment of Muscles. To two : the Flexor brevis minimi digiti, and the 

 Flexor ossis metacarpi minimi digiti ; and to the anterior annular ligament. 

 10 



