THE KADIO-ULNAR ARTICULATION THE CARPAL ■ JOINTS 221 



joints and also pouches downward under the origins of the flexors of the digit and 

 the lateral flexor of the carpus. There are two collateral ligaments. 



_ The medial Ugament (Lig. coUaterale radiale) is attached above to an 

 eminence on the medial epicondyle of the humerus, and divides into two parts- 

 the long, superficial part ends on the medial border of the radius, just below the 

 level of the interosseous space; the deep, short part is inserted into the medial tu- 

 berosity of the radius. 



The lateral Ugament (Lig. collateral ulnare) is short and strong. It is at- 

 tached above to a depression on the lateral epicondyle of the humerus, and below 

 to the lateral tuberosity of the radius, just below the margin of the articular surface. 

 Movements.— This joint is a typical ginglymus, the only movements being 

 flexion and extension around an axis which passes through the proximal attachments 

 of the collateral ligaments. In the standing position the articular angle (in front) is 

 about 140° to 150°. The range of movement is about 55° to 60°. Complete ex- 

 tension is prevented chiefly by the tension of the collateral ligaments and the biceps 

 muscle. (The axis of movement is slightly oblique, so that in flexion the forearm 

 is carried somewhat outward.) 



THE RADIO-ULNAR ARTICULATION 



In the foal the shaft of the ulna is attached to the radius above and below the 

 interosseous space by the interosseous ligament of the forearm (Lig. interosseum 

 antibrachii). Below the space the two bones become fused before adult age is 

 reached. Above the space the ligament usually persists, but may undergo more 

 or less ossification in extreme old age. The transverse or arciform ligament (Lig. 

 transversum ulnare et radiale ulnae et radii) consists of fibers which pass above the 

 interosseous space from each border of the shaft of the ulna to the posterior sur- 

 face of the radius. The proximal radio-ulnar articulation (Articulatio radio-ulnaris 

 proximalis), formed by two small convex facets on the ulna and the corresponding 

 facets on the posterior surface of the proximal extremity of the radius, is inclosed 

 in the capsule of the elbow-joint and does not require separate consideration. The 

 distal extremity of the ulna fuses early with the radius, and is therefore regarded 

 usually as a part of the latter. 



Movement. — This is inappreciable, the forearm being fixed in the position of 

 pronation. 



THE CARPAL JOINTS 



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

 is popularly termed the "knee-joint" in animals.^ This consists of three chief 

 joints, viz., (1) The radio-carpal or antibrachio-carpal joint (Articulatio radiocarpea) 

 formed by the distal end of the radius and the proximal row of the carpus; (2) the 

 intercarpal joint (Articulatio inter carpea), formed between the two rows of the car- 

 pus; (3) the carpo-metacarpal joint (Articulatio carpometacarpea), formed between 

 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 addi- 

 tion there are arthrodial joints formed between adjacent bones of the same row 

 (Articulationes interossese). All these form a composite joint with numerous liga- 

 ments. The articular surfaces have been described in the Osteology. 



The joint capsule may be regarded, so far as the fibrous part is concerned, as 

 being common to all three joints. It is attached close to the margin of the articu- 



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

 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. 



