TRAPEZOIDES OS MAGNUM. 



Ill 



oackwards, 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 in eta- 

 carpi ; 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 surfaces 

 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 angu- 

 lar in the middle, and is often marked by a small rough depression, "for 

 an interosseous ligament ; the two remaining sides are flat, 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 up- 

 wards, and the concavo-convex surface forwards, the angular concave 

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



Articulations. VJithfour bones; by the concavo-convex surface, with 

 the second metacarpal bone ; by the angular concave surface, w r ith the os 

 magnum ; and by the other two surfaces, with the trapezium 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 ex- 

 tremity 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. With seven bones ; by the 

 rounded head, with the cup formed by the sca- 

 phoid 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. 



* The hand viewed upon its anterior or palmar aspect. 1. The scaphoid bone. 2. 

 The semilunare. 3. The cuneiforme. 4. The pisiforme. 5. The trapezium. 6. Tun 

 groove in the trapezium that lodges the tendon of the flexor carpi radialis. 7. The 

 trapezoides. 8. The os magnum. 9. The unciforme. 10, 10. The five metacarpa' 

 bones. 11, 11. The first row of phalanges. 12, 12. The second row. 13, 13. Tho 

 third row, or nngual phalanges. 14. The first phalanx cf the thumb. 15. The second 

 and la*t phalanx of the thumb. 



