268 



THE ARTICULATIONS 



sion — circumduction. Lacking only rotation on a vertical axis, it thus possesses most of the 

 movements of a ball-and-socket joint, without the weakness and liability to dislocation which 

 are pecuhar to these joints. This deficiency of rotation is compensated for by the movements 

 of the radius at the radio-ulnar joints, viz., supination and pronation. Its strength depends 

 chiefly upon the number of tendons which pass over it, and the close connection which exists 

 between the fibrous tissue of their sheaths and the capsule of the wrist; also upon the proximity 

 of the medio-carpal and carpo-metacarpal joints, which permits shocks and jars to be shared 

 and distributed between them; another source of strength is the absence of any long bone on the 

 distal side of the joint. In flexion and extension the carpus rolls backward and forward, respec- 

 tively, beneath the arch formed by the radius and articular disc; flexion being limited by the 

 dorsal ligament and dorsal portions of the collateral; extension by the volar, and volar portions 

 of the collateral ligaments. In adduction and abduction the carpal bones glide from the ulnar 

 to the radial side and from the radial to the ulnar side, respectively. Abduction is more limited 

 than adduction, and is checked by the ulnar collateral ligament and by contact of the styloid 

 process of the radius with the greater multangular; adduction is checked by the radial collateral 

 ligament alone. One reason for adduction being more free than abduction is that the ulna does 



Fig. 302. — Front of Wrist with Transverse Carpal Ligament. 



Anterior radio-ulnar 



ligament i^vm 



Ulnar collateral ligament of 

 wrist with slip to annu- 

 lar ligament 



Pisiform 



Transverse carpalligament 



Volar radio-carpal ligament 



Tendon of the flexor carpi 

 radialis 



not reach so low down as the radius, and the yielding articular disc allows of greater movement 

 upward of the ulnar end of the carpus. In circumduction the hand moves so as to describe a 

 cone, the apex of which is at the wrist. These movements are made more easy and extensive 

 by the sliglit gliding of the carpal bones upon one another, and the comparatively free motion 

 at the medio-carpal joint. The oblique direction of the fibres of the collateral ligaments pre- 

 vents any rotation at the radio-carpal joint, while it permits considerable freedom of abduction 

 and adduction. 



Muscles which act upon the radio-carpal joint. — Flexors. — The flexors of the carpus and 

 the long flexors of the fingers and the tlmmb, and the palmaris longus. Extensors. — The exten- 

 sors of the carpus and fingers. Abductors. — Extensor carpi radialis longus, the abductor pol- 

 licis longus (extensor ossis incfacarpi pollicis. Adductors. — Flexor carpi ulnaris, extensor carj)! 

 ulnaris. 



7. THE CARPAL JOINTS 



The joints of the carpus may be subdivided into — 



(a) The joints of the first row. 



(b) The joints of the second row. 



(c) The medio-carpal, or junction of the two rows with each other. 



