86 



BONES OF THE UPPER LIMB. 



internal inferior angle. On the external side beneath the surface for the 

 scaphoid is a short surface for the trapezoid bone ; and on the internal 

 surface is a vertically elongated surface which articulates with the uncifonn 

 bone. Inferiorly this bone articulates by three distinct surfaces, of which 

 the middle is much the largest, with the second, third, and fourth metacarpal 

 bones. The os magnum articulates with seven bones, viz., the scaphoid, 

 semilunar, trapezoid, unciform, and second, third, and fourth metacarpal bones. 



THE UNOIFORM BONE. 



The unciform bone is readily distinguished by the large process projecting 

 forwards and curved slightly outwards on its anterior surface. Seen from 

 the front or behind, it has a triangular form. Its external surface is ver- 

 tical, and articulates with the os magnum ; its inferior surface is divided 

 into two facets which articulate with the fourth and fifth metacarpal bones ; 

 its superior surface, meeting the cuneiform, is concavo-convex, inclines 

 upwards and outwards towards the head of the os magnum, and is separated 

 internally by a rough border from the inferior surface. The unciform 

 articulates with five bones, viz., the os magnum, semilunar, cuneiform, and 

 fourth and fifth metacarpal bones. 



THE METACARPUS. 



The metacarpus, the part of the hand which supports the fingers, consists 

 of five shafted bones, which are numbered from without inwards. These 

 bones are placed in a slightly arched plane, and are nearly parallel one with 

 the other, with the exception of the first, which diverges from the second. 



Fig. 77. 



Fig. 77. THE RIGHT HAND FROM BEFORE. 



5, scaphoid bone ; I, semilunar ; c, cuneiform ; 

 p, pisiform ; t, trapezium ; next it the trape- 

 zoid, not lettered ; next the os magnum, also not 

 lettered ; u, unciform. 



I to V, the metacarpal bones j 1, 3, first and 

 second phalanges of the thumb; 1, 2, 3, the 

 first, second, and third phalanges of the little 

 finger, and similarly for the other three fingers, 

 not marked ; *, one of the sesamoid bones of the 

 thumb seen sidewise. 



The metacarpal bones are slightly 

 curved, so as to present a concavity 

 directed forwards. They are terminated 

 at their carpal extremities by expanded 

 portions of different forms, and at the 

 digital ends by large rounded heads. 

 The first metacarpal bone is thicker and 

 shorter than the others. Of the remain- 

 ing bones the third is the longest and 

 thickest, and the second, fourth, and fifth 

 decrease regularly in length, according to 

 their position from without inwards. 



The shaft of the first metacarpal bone is somewhat compressed from 

 before backwards, flat behind, and transversely convex in front. The 

 shafts of the others are prismatic, presenting a broad surface towards 

 the back of the hand, and towards the palm a rounded margin between 

 the two lateral surfaces. They are most slender immediately beyond the 

 carpal extremity, and become gradually thicker towards the head. They 



