240 THE AfrnccLATioys 



from the scaplinid to the cuneiform hone; hesides hinding down the head of the 

 magnum, it serves to fix the upper and outer angle of the unciform in the socket 

 formed l»y the lirst row. 



The dorsal ligaments, like the palmar, are strengthened by a tjuantity of fibrous 

 tissue l)elonging to the sheaths of the extensor tendons, and by an extension of 

 some of the fibres of the capsule of the wrist. There are no proper lateral medio- 

 carpal ligaments; they are luit prolongations of the lateral ligaments of the wrist. 



Tlie synovial membrane (fig. 285) of the carpus is common to all the joints of 

 the carjius. and exti'uds to the bases of the four inner metacarpal bones. Thus, 

 besides lining the inter- or medio-carpal joint, it sends two processes upwards 

 l)etween the three bones of the first row, and three downwards between the con- 

 tiguous surfaces of the trai)ezoid and trapezium, the trapezoid and magnum, and 

 magnum and unciform. From these latter, prolongations extend to the four inner 

 carpo-metacar))al joints and the three intermetacarpal joints. 



The arterial supply is derived from (a) the anterior and posterior carpal 

 branches of the radial and ulnar arteries; (6) the carpal branch of the anterior 

 interosseous; (c) the recurrent branches from the deep palmar arch. The terminal 

 twigs of the anterior and posterior interosseous arteries supply the joint on its dorsal 

 aspect. 



Th(^ nerve-supply comes from the ulnar on the ulnar side, the median on the 

 radial side, and tlie posterior interosseous behind. 



The movements of the carpal articulations between bones of the same row are 

 very limited and consist only of slight gliding upon one another; but, slight as they 

 are, they give elasticity to the carpus to break the jars and shocks Avhich result 

 from blows or falls upon the hand. 



The movements of one row of bones upon the other at the medio-carpal joint 

 are more extensive, especially in the direction of flexion and extension, so that the 

 hand enjoys a greater range of these movements than is permitted at the wrist-joint 

 alone. At the wrist, extension is more free than flexion; but this is balanced by 

 the greater freedom of flexion than of extension at the medio-carpal joint, and by 

 flexion at the carpo-metacarpal joint, so that on the whole the range of flexion of 

 the hand is greater than that of extension. 



A slight amount of lateral motion accompanied by a limited degree of rotation 

 also takes place; this rotation consists in the head of the magnum and the superior 

 and outer angle of the unciform bone rotating in the socket formed by the three 

 bones of the upper row, and in a gliding forwards and backwards of the trapezium 

 and trapezoid upon the scaphoid. 



In addition to the ligaments, the undulating outline and the variety of shapes of 

 the apposed facets render this joint very secure. 



Bearing in mind the mobility of this medio-carpal joint and of the carpo- 

 metacarpal, Ave see at once the reason for the radial and ulnar flexors and extensors 

 of the caqjus being prolonged down to their insertion into the base of the meta- 

 carpus, for they produce the combined effect of motion at each of the three 

 transverse articulations: (1) at the wrist; (2) at the medio-carpal; (3) at the 

 carpo-metacarpal joints. 



8. THE CARPO-METACARPAL JOINTS 

 These may l)e divided into two sets, namely: — 



(a) The carpo-metacarpal joints of the four inner fingers. 

 (/)) The carpo-metacarpal joint of the thumb. 



The inferior surfaces of three of the bones of the second row of the carpus 

 present a composite surface for the four inner metacarpal bones; the trapezium 

 presents a distinct and separate saddle-shaped surface for the base of the meta- 

 carpal bone of the thumb. 



