THE CARPAL JOINTS 



271 



from it by the transverse carpal ligament, and the radial artery passes across its lateral border 

 mstead of m front. 



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

 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 which 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 m the direction of flexion and extension, so that the hand enjoys a greater 

 range of these niovements 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 jomt, 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. 



Fig. 304. — Synovial Membraxes of Wrist, Hand, and Fingers 



Synovial sac of the infe 

 nor radio-ulnar joint 



Synovial sac of the carpus 



Synovial sac, occasionally 

 separate, for the fourth 

 and fifth metacarpal bones 



-Synovial sac of the wrist-joint 



.Synovial sac of the carpo-meta 

 carpal joint of the thumb 



Collateral ligaments of the metacarpo- 

 piialangeai and interphalangeal 



joints 



A slight amount of side to side motion accompanied by a hmited degree of rotation also 

 f^ P^ce; this rotation consists in the head of the capitate and the superior and lateral angle 

 of the hamate bone rotating in the socket formed by the three bones of the upper row, and in^a 

 ghding forward and backward of the greater and lesser multangular upon the navicular. 



In addition to the hgaments, the undulating outline and the variety of shapes of the apposed 

 facets render this joint very secure. 



Bearing in mind the mobihty of this medio-carpal joint and of the carpo-metacarpal, we see 

 at once the reason for the radial and ulnar flexors and extensors of the carpus being prolonged 

 down to their insertion into the base of the metacarpus, 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. 



Muscles which act upon the mid-carpal joint. — The muscles which act upon this joint are 

 the same as those which act upon the radio-carpal joint, except the flexor carpi ulnaris, which is 

 inserted into the pisiform bone. 



