236 



THE ARTICr'LATIOXS 



around an antero-postorior axis, i.e. abduction and adduction; together with a 

 combination of these in quick succession — circuni(Uiction. 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 peculiar to these 

 joints. This deficiency of rotation is compensated for by the movements of the 

 radius at the radio-ulna'r joints, viz. supination and pronation. Its strength depends 

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

 whicli 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 lietween 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 forwards and backwards l^eneath the arch formed by 



Fig. 233.— Fkoxt of Wkist with Anteriok .\nnular Ligament. 



Anterior radio-ulnar 

 ligament 



Internal lateral ligament of 

 wrist with slip to annular 

 ligament 



Anterior annular ligament 



Anterior radio-carpal 

 ligament 



Tendon of the flexor 

 carpi radialis 



the radius and fibro-cartilage; flexion being limited l)y the posterior ligament and 

 posterior portions of the lateral; extension l)y the anterior, and anterior portions 

 of the lateral ligaments. In adduction and abduction, the carpal bones glide 

 from without inwards and from within outwards. Abduction is more limited 

 than adduction, and is checked by the internal lateral ligament and by contact 

 of the styloid process of the radius with the trapezium; adduction is checked by 

 the external lateral ligament alone. One reason for adduction being more free 

 than aV)duction is that the ulna does not reach so low down as the radius, and the 

 yielding filiro-cartilage allows of greater movement upwards of the inner end of the 

 carpus. In circumduction the hand moves so as to describe a cone, the apex of 

 wliich is at the wrist. These movements are made more easy and extensive by the 

 slight gliding of the carpal bom-s upon one another, and the comparatively free 

 motion at the medio-cari)al joint. The ol)li(][ue direction of the fibres of the lateral 



