102 



THE BONES OF THE UPPER LIMB. 



Fig. 105. RIGHT TRAPEZIUM, 



FROM BEFORE. (G. D. T. ) 



bone : this surface does not extend the whole length of the pisiform bone, but 

 leaves a small free projecting portion below. The inner side of the bone is 

 generally convex and somewhat rough. The outer side is smoother and slightly 

 concave. 



The trapezium is the most external of the second row of carpal bones. It 

 presents a rhombic form when seen in its dorsal or palmar aspect, but with the 

 lower angle much produced and truncated. Its anterior surface is marked by a 

 vertical groove traversed by the tendon of the flexor carpi radialis muscle, and 



externally to the groove by a ridge or tulerosity, one of 

 the four prominences which give attachment to the an- 

 terior annular ligament. Of the internal sides of the 

 rhomb, the superior articulates with the scaphoid and 

 the inferior with the trapezoid ; while a small facet 

 on the prominent lower angle is for the second meta- 

 carpal bone. Of the external sides, the superior is free, 

 and the inferior presents a smooth surface, convex from 

 behind forwards, and concave from without inwards, 

 which articulates with the metacarpal bone of the thumb, 

 and is separated by a small interval from the surface 

 for the second metacarpal bone. The trapezium articu- 

 lates with four bones, viz., the scaphoid, trapezoid, 

 and first and second metacarpals. 



The trapezoid bone is considerably smaller than 

 the trapezium. Its longest diameter is from before 

 backwards. Its posterior free surface is much larger 

 than the anterior. The external inferior angle of the 

 anterior surface is distinguished by being prolonged a 

 little backwards between the articular surfaces for the 

 trapezium and second metacarpal bone. The superior 

 surface articulates with the scaphoid ; 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, nearly rectangular below, rounded above. The upper extremity or head 



articulates superiorly with the lunar 

 bone by a convex surface, extending 

 farther down behind than in front, 

 and prolonged on the outer side for 

 the scaphoid. A neck is formed 

 beneath by depressions on the an- 

 terior and posterior surfaces. The 

 anterior surface of the bone is much 

 narrower than the posterior. The 

 posterior surface projects downwards 

 at its internal inferior angle. On 

 the outer side, below the surface 

 for the scaphoid, is a short surface 

 for the trapezoid bone ; and on the 

 inner side is a vertically elongated surface which articulates with the unciform 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 



Fig. 106. RIGHT TRAPEZOID 



BONE : PALMAR ASPECT. 



(<J. D. T.) 



Fig. 107. RIGHT os MAGNUM : A, INNER VIEW: 



]3, OUTER VIEW. (G. D. T.) 



