THE CARPAL JOINTS 



183 



THE CARPAL JOINTS 



Those joints taken together constitute the composite articulatio carpi, or what 

 is popuhu'h' termed the "knee-joint" in animals.' This consists of three chief 

 joints, viz., (1) The radio-carpal joint, formed by the distal end of the radius and 

 the proximal row of the carpus; (2) tlie intercarpal joint, formed between the two 

 rows of the carpus; (3) tlie carpo-metacarpal joint, formed l^etween the distal row 

 of the carpus and the proximal ends of the metacarpal bones. The proximal and 

 middle joints may be regarded as ginglymi, although they are not typical or pure 

 examples of hinge-joints. The distal joint is arthrodial. In addition there are 

 arthrodial joints formed between adjacent bones of the same row (Articulationes 

 interossese). All these constitute a very composite joint, with numerous ligaments. 

 The articular surfaces have been described 

 in the Osteology. 



The joint capsule may l)e regarded, 

 so far as the fibrous ])art is concerned, as 

 being common to all three joints. It is 

 attached close to the margin of the articuT 

 lar surface of the radius above and the 

 metacarpus below; its deep face is also 

 attached to a considerable extent to the 

 carpal bones and to the small ligaments. 

 Its anterior part, the dorsal or anterior 

 common ligament, is rather loose, and 

 assists in forming the fibrous canals for 

 the extensor tendons. Its posterior part, 

 the volar or posterior common ligament, 

 is very thick and dense, and is closel}^ 

 attached to the carpal bones. It levels 

 up the irregularities of the skeleton here, 

 and forms the smooth anterior wall of the 

 carpal canal. It is continued downward 

 to form the subcarpal or inferior check 

 ligament, which blends with the tendon of 

 the flexor perforans about the middle of 

 the metacarpus. 



The synovial membrane forms three 

 sacs corresponding to the three joints. 

 The radio-carpal sac is the most volum- 

 inous; it includes the joints formed by the 

 accessory carpal bone, and also those be- 

 tween the proximal carpal bones as far as the interosseous ligaments. The 

 intercarpal sac sends extensions upward and downward between the bones of 

 the two rows as far as the interosseous ligaments; it communicates between 

 the third and fourth carpal bones with the carpo-metacarpal sac. The latter is 

 very limited in extent, and is closely applied to the bones; it incloses the carpo- 

 metacarpal joint, and lubricates also the lower parts of the joints between the 

 distal carpal bones and the intermetacarpal joints. 



The external lateral ligament (Ligamentum carpi collaterale ulnare) is attached 

 above to the external tuberosity of the distal end of the radius. Its long superficial 

 part is attached below to the proximal end of the external small metacarpal chiefly, 



' The term is a very unfortunate one, since it is a distinct misapplication of the name as it ia 

 used in regard to man. It is, however, very firmly established, and appears likely to persist in- 

 definitely in the absence of a convenient popular equivalent. 



Fig. 146. — Frontal Section of Carpal Joints of 

 Horse (Right Side). 

 /.);., External, l.r., internal, lateral ligament; 

 Cr, radial carpal; Ci, intermediate carpal; Cu, ulnar 

 carpal; C2, second carpal; CS, third carpal; C4, 

 fourth carpal; Mc2, second (internal) metacarpal; 

 Mc3, third (large) metacarpal; Mc4, fourth (exter- 

 nal) metacarpal. 



