132 



THE SKELETON 



metacarpal, the upper and larger for the trapezoid. The radial and dorsal sur- 

 faces are r()U<rh for li<j;anients.' The palmar surface i)re8ents a prominent ridge, 

 Avhieli has to its ulnar side a deep groove which transmits the tendon of the fexor 

 carpi radial is. To the ridge of the trapezium the anterior annular ligament is 

 attached. The palmar surface affords attachment to the abductor, flexor ossis, flexor 

 brer is, and sometimes a ])ortion of the extensor os-ns metacarpi pollicis. 



Articulations. — With the scaphoid, trapezoid, and the first and second meta- 

 carjial l)ones. 



The TRArEzoiD 



The trapezoid is also very irregular in shape, and much smaller than the 

 trapezium. It has a broad dorsal surface; the narrow palmar surface gives 

 origin to a few fibres of the inner head of the/<'.ror brer is pollicis. The portion of 



Fig. 141.— The Left Trapezoid. 



palmar surface . 



for trapezium 

 for second metacarpal 



l)(jne between these surfaces is constricted and mapped out into articular facets; of 

 these, the inferior is most conspicuous; it is sacldle-shaped for the base of the 

 second metacarpal. The radial surface has a facet for the trapezium; the ulnar 

 surface is articular for the magnum; and the superior surface has a facet for the 

 seajjlioid. 



Articulations. — With the trapezium, magnum, scaphoid, second metacarpal. 



The Magnum 



The magnum is the largest carpal bone, and occupies the centre of the wrist. 

 The superior surface is globular, and sometimes called the head. It is received 

 into the cup formed by the semilunar and scaphoid. The articular surface of the 

 head extends some distance on to the dorsal aspect of the bone. The inferior 

 surface has three facets. The middle is the largest for the base of the third meta- 

 ear])al. The small ulnar facet is for the fourth, and the radial facet is for the 

 second metacarpal. The outer (radial) surface articulates with the trapezoid, and 



Fig. 142.— The Left Magnuji. 



FOR SEMILUNAR 

 FOR SCAPHOID 



THE RADIAL OR OUTER 

 SIDE 



FOR SECOND METACARPAL 

 FOR THIRD METACARPAL 



FOR SEMILUNAR 

 FOR UNCIFORM 



THE ULNAR OR INNER 

 SIDE 



FOR FOURTH METACARPAL 



j.resents al)ove this small facet a deep groove for an interosseous ligament. The 

 inner (ulnar) surface of the heme has a long articular surface for the unciform 

 (sometimes the lower part of tliis surface forms a detached facet), but is rough 

 near its anterior ])art for hgaments. The palmar surface is convex and rougli, 

 and affords origin to the inner head of the flexor brevis pollicis. The rough dorsal 

 surface is broad, and has a dee]) concavity, which serves to make the head of the 

 bone more i)romiuent, and gives rise to the appearance of a neck. 



Articulations.— Trapezoid, unciform, semilunar, scaphoid, and second, third, 

 and fourth n)etacarpals. 



