TRAPEZOIDES. OS MAGNUM. 85 



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, abductor pollicis and flexor ossis 

 metacarpi ; and by the tubercle, to the annular ligament. 



The TRAPEZOIDES (os multangulum minus) is a small, oblong, and 

 quadrilateral bone, bent near its middle upon itself (bean-shaped). It 

 presents four articular surfaces and two extremities. One of the sur- 

 faces is concavo-convex, i. e. concave 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 

 fiat, 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-convex surface forwards, the angular con- 

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



Articulations. With four 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 (capitatum) is the largest bone of the carpus, and 

 is divisible into a body and head. The head is round for the greater 

 part of its extent, but is flattened on one side. The body is irregularly 

 quadrilateral, and presents four sides and a smooth extremity. Two 

 of the sides are rough, the one being square and flat, the dorsal, the 

 other rounded and prominent, the palmar ; the other two sides are 

 articular, the one being concave, the other convex. The extremity is 

 a triangular articular surface, divided into three facets. 



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

 look upwards and the broad dorsal surface backwards (towards the 

 holder), the concave articular surface will point to the hand to which 

 the bone belongs. 



Articulations. \Vith seven bones ; by the rounded head, with the 

 cup formed by the scaphoid and semilunar bone ; by the side of the 

 convex surface, with the trapezoides ; by the concave surface, with the 

 unciforme ; and by the extremity, with the second, third, and fourth 

 metacarpal bones. 



Attachments. To the flexor brevis pollicis muscle. 



