92 



BONES OF THE UPPER LDIB. 



circular facet on its outer half, which articulates with the pisiform bone, 

 The cuneiform articulates with three bones, viz., the semilunar, pisiform, 

 and unciform. 



The pisiform bone lies on a plane anterior to the other bones of the 

 carpus. Posteriorly it possesses an articular surface, which rests on the 

 Cuneiform bone. The mass of the bone is so inclined from this surface 

 downwards and outwards, that the pisiform bone of one hand is distin- 

 guishable from that of the other. 



The trapezium bone is the most external of the second row of 

 carpal bones. It presents a rhombic form when seen in its dorsal or 

 palmar aspect, and has its most prominent angle directed downwards. 



Fig. 78. Fig. 78. — Dorsal View of the CARrus, with a 



PORTION OF EACH OF THE METACARPAL BoNES. -^ 



1, scaplioid ; 2, semilunar ; 3, cuneiform ; 4, 

 pisiform ; 5, trapezium ; 7, tiapezoid ; S, os mag- 

 num ; 9, unciform. 



Its anterior surface is marked by a 

 vertical groove traversed by the tendon 

 of the flexor carpi radialis muscle, and 

 external to the groove by a ridge, or 

 tubercle, one of the four prominences 

 which give attachment to the anterior 

 annular ligament. Of the internal sides 

 of the rhomb, the superior articulates with the scaphoid bone, the inferior 

 with the trapezoid bone, and by a small facet close to the inferior angle 

 also with the second metacarpal bone. Of the external sides the supe- 

 rior is rough, and the inferior presents a smooth surface, convex from 

 behind forwards, and concave from without inwards, which articulates 

 with the metacarpal bone of the thuml), and is separated by a rough 

 line at the inferior angle from the surface for the second metacarpal 

 bone. The trapezium articulates with foiu- bones, viz., the scaphoid, 

 tra]iezoid, and first and second metacarpals. 



The trapezoid bone is considerably smaller than the trapezimn. 

 Its longest diameter is from before backwards. Its posterior surface, 

 which is pentagonal, is much larger than the anterior. The external 

 inferior angle of the anterior surface is distinguished by being pro- 

 longed a little backwards between the trapezium and second metacarpal 

 bone. The superior surface articulates with the scaphoid bone ; the 

 external with the trapezium ; the internal with the os magnum ; and 

 the inferior by a large surface convex from side to side with the second 

 metacarpal bone. The trapezoid articulates with four bones, viz., the 

 scaphoid, trapezium, os magnum, and second metacarpal bone. 



The OS magnum is the largest of the carpal bones. In form it is 

 elongated vertically, rectangular interiorly, rounded superiorly. The 

 articular surfece of the superior extremity or Jieail is prolonged on the 

 outer, but not on the inner side, and is continued further down behind 

 than in front. A ncrJc is formed beneath by depressions on the anterior 

 and posteiior surfaces. The anterior surface of the bone is much nar- 

 rower thar«. the posterior. The posterior surface jirojects downwards 

 at its internal inferior angle. On the outer side beneath the surface 

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

 inner side is a vertically elongated surface Avhich articulates with 



