58 LAMENESS OF THE HORSE 



Undue extension, (by extension is meant such movement as 

 will cause the long axis of two articulating bones to assume a 

 position which approaches or forms a straight line — opposite to 

 flexion), of the scapulohumeral joint is impossible while weight 

 is borne, because of the normally flexed position of the humerus 

 on the scapula ; whereas flexion, beyond desirable limits, is in- 

 hibited by the biceps braehii (flexor l)rachii or coracoradialis) 

 muscle. 



The distal end of the humerus, however, articulating with the 

 radius and ulna in a fashion that no support is lent liy any sort 

 of contact with the liody, is a ginglymus (hinge) joint and later- 

 al motion, because of the long transverse diameter of its articular 

 ]")ortions, is easily prevented by the medial and lateral ligaments 

 (internal and external ligaments). Flexion of this, the humero- 

 radioulnar joint (elbow), is restrained by the triceps braehii 

 and extension is checked by the biceps braehii (flexor braehii). 



The carpal joint (erroneously called the knee joint), is com- 

 posed of the several carpal bones which interarticulate and, 

 when taken as a group, serve as a means of attachment and ar- 

 ticulation for the radius and metacarpal bones. 



The transverse diameter of this joint is long, thus giving it 

 contacting surfaces that are sufiiciently extensive to minimize 

 the strain upon the mesial and lateral ligaments (internal and 

 external lateral common ligaments). ]\Iotion is that of flexion 

 and extension ; slight rotation is possible when the position is 

 that of flexion. While supporting weight the carpus is fixed in 

 position by a slight dorsal flexion, but undue dorsal flexion is 

 prevented by the flexor muscles and tendons and volar-carpal or 

 annular ligament, together with the superior cheek ligament. 



The metacarpophalangeal articulation (fetlock joint), is a 

 hinge joint and its articular surfaces contact one another, with 

 respect to their having a long bearing surface from side to side, 

 as do all ginglymus (hinge) joints. Two common lateral liga- 

 ments bind the bones together. AVhile bearing weight, there is 

 assumed a position of slight dorsal flexion, undue flexion being 

 checked by the inhibitory ap])aratus of the joint — cheek liga- 

 ments, and their tendons and the suspensory ligament. The in- 

 hibitory apparatus of the fetlock joint is materially reinforced 



