CARPO-METACARPAL ARTICULATIONS. 265 



two joints : (1) the superior (wrist-joint proper), between the meniscus and bones 

 of the forearm ; (2) the inferior, between the hand and meniscus (transverse or 

 mid-carpal joint). 



(1) The articulation between the forearm and carpus is a true condyloid artic- 

 ulation, and therefore all movements but rotation are permitted. Flexion and 

 extension are the most free, and of these a greater amount of extension than flexion 

 is permitted on account of the articulating surfaces extending farther on the dorsal 

 than on the palmar aspect of the carpal bones. In this movement the carpal 

 bones rotate on a transverse axis drawn between the tips of the styloid processes 

 of the radius and ulna. A certain amount of adduction (or ulnar flexion) and 

 abduction (or radial flexion) is also permitted. Of these the former is considerably 

 greater in extent than the latter. In this movement the carpus revolves upon an 

 antero-posterior axis drawn through the centre of the wrist. Finally, circumduction 

 is permitted by the consecutive movements of adduction, extension, abduction, and 

 flexion, with intermediate movements between them. There is no rotation, but 

 this is provided for by the supination and pronation of the radius on the ulna. 

 The movement of flexion is performed by the Flexor carpi radialis, the Flexor 

 carpi ulnaris, and the Palmaris longus ; extension, by the Extensor carpi radialis 

 longior et brevior and the Extensor carpi ulnaris ; adduction (ulriar flexion), by the 

 Flexor carpi ulnaris and the Extensor carpi ulnaris ; and abduction (radial flexion), 

 by the Extensors of the thumb and the Extensor carpi radialis longior et brevior 

 dnd the Flexor carpi radialis. 



(2) The chief movements permitted in the transverse or mid-carpal joint are 

 flexion and extension and a slight amount of rotation. In flexion and extension, 

 which is the movement most freely enjoyed, the trapezium and trapezoid on the 

 radial side and the unciform on the ulnar side glide forward and backward on the 

 scaphoid and cuneiform r-espectively, while the head of the os magnum and the 

 superior surface of the unciform rotate in the cup-shaped cavity of the scaphoid 

 and semilunar. Flexion at this joint is freer than extension. A very trifling 

 amount of rotation is also permitted, the head of the os magnum rotating round a 

 vertical axis drawn through its own centre, while at the same time a slight gliding 

 movement takes place in the lateral portions of the joint. 



IX. Carpo-metacarpal Articulations. 



1. ARTICULATION OF THE METACARPAL BONE OF THE THUMB WITH THE 



TRAPEZIUM. 



This is a joint of reciprocal reception, and enjoys great freedom of movement, 

 on account of the configuration of its articular surfaces, which are saddle-shaped, 

 so that, on section, each bone appears to be received into a cavity in the other, 

 according to the direction in which they are cut. The joint is surrounded by a 

 capsular ligament. 



The Capsular Ligament is thick, but loose, and passes from the circumference 

 of the upper extremity of the metacarpal bone to the rough edge bounding the 

 articular surface of the trapezium ; it is thickest externally and behind, and lined 

 by a separate synovial membrane. 



Movements. In the articulation of the metacarpal bone of the thumb with the 

 trapezium the movements permitted are flexion, extension, adduction, abduction, 

 and circumduction. When the joint is flexed the metacarpal bone is brought in 

 front of the palm and the thumb is gradually turned to the fingers. It is by this 

 peculiar movement that the tip of the thumb is opposed to the other digits ; for 

 by slightly flexing the fingers the palmar surface of the thumb can be brought in 

 contact with their palmar surfaces one after another. 



