TRAPEZIUM TRAPEZOIDES. 81 



rounded, and the remaining sides are, one slightly concave, the 

 other slightly convex. 



If the bone be held so that the- articular facet shall look down- 

 wards, and the extremity which overhangs the articular facet 

 forwards, the concave side will point to the hand to which it 

 belongs. 



Articulations. With the cuneiform bone only. 



Attachments. To two muscles the flexor carpi ulnaris, and 

 abductor minimi digiti ; and to the annular ligament. 



The trapezium is too irregular in form to be compared to any 

 known object ; it may be distinguished by a deep groove for the 

 tendon of the flexor carpi radialis muscle. It is somewhat com- 

 pressed, and may be divided into two surfaces which are smooth 

 and articular, and three rough borders. One of the articular sur- 

 faces is oval, concave in one direction, and convex in the other ; 

 the other is marked into three facets. One of the borders presents 

 the groove for the tendon of the flexor carpi radialis, which is sur- 

 mounted by a prominent tubercle for the attachment of the annular 

 ligament ; the other two borders are rough and form the outer side 

 of the carpus. The grooved border is narrow at one extremity 

 and broad at the other, where it presents the groove and tubercle. 



If the bone be held so that the grooved border look upwards 

 while the apex of this border be directed forwards, and the base 

 with the tubercle backwards, the concavo-convex surface will 

 point to the hand to which the bone belongs. 



Articulations. With four bones; by the concavo-convex surface, 

 with the metacarpal bone of the thumb ; and by the three facets of 

 the other articular surface, with the scaphoid, trapezoid, and second 

 metacarpal bone. 



Attachments. To two muscles flexor ossis metacarpi, and flexor 

 brevis pollicis ; and by the tubercle, to the annular ligament. 



The trapezoides is a small, oblong, and quadrilateral bone, bent 

 near its middle upon itself. It presents four articular surfaces and 

 two extremities. One of the surfaces is concavo-convex, i. e. con- 

 cave in one direction and convex in the other ; another, contiguous 

 to the preceding, is concave, so as to be almost angular in the 

 middle, and is often marked by a small rough depression, for an 

 interosseous ligament ; the two remaining sides are J?aZ, and present 

 nothing remarkable. One of the two extremities is broad and of 

 large size, the dorsal ; the other, or palmar, is small and rough. 



If the bone be held perpendicularly, so that the broad extremity 

 be upwards, and the concavo-cohvex surface forwards, the angular 

 concave surface will point to the hand to which the bone belongs. 



Articulations. Wiihfour bones ; by the concavo-convex surface, 

 with the second metacarpal bone ; by the angular concave surface, 

 with the os magnum; and by the other two surfaces, with the trape- 

 zium and scaphoid. 



Attachments. To the flexor brevis pollicis muscle. 



The os magnum is the largest bone of the carpus, and is divisible 



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