60 LAMENESS OF THE HORSE 



of about 50 to 55 degrees from a horizontal plane while weight 

 is being supported. Its distal end articulates with the second or 

 median phalanx (os corona) and forms the proximal inter- 

 phalangeal (pastern or sutfraginocoronary) joint. This also, 

 is a gingiymus joint, having but slight lateral motion, and that 

 only when it is in a state of flexion. A rather broad articular 

 surface — from side to side — exists here, lessening the strain 

 on the collateral ligaments somewhat. Dorsal flexion is checked 

 by the flexor tendons and dorsal ligaments. Volar flexion is re- 

 strained by the extensor tendons. 



The distal end of the second phalanx (os corona) has but slight 

 lateral motion and this is manifested principally when it is in 

 a state of volar flexion. Undue dorsal flexion is prevented by 

 the deep flexor tendon (perforans) and volar flexion is inhibited 

 by the extensor of the digit (extensor pedis). Thus it is seen, 

 that when the leg is a weight-bearing member, weight is sup- 

 ported by the hony framework whose constituent parts are joined 

 together by ligaments and tendons and each one of the several 

 bones articulates in such manner that the joint is locked. The 

 articular parts of bones rest upon or against an inhibitory ap- 

 paratus, and are slightly flexed, as in the carpus, or considerably 

 flexed such as in the fetlock joint when weight is being sup- 

 ported. In the first instance, for example, the flexors of the 

 carpus and the superior check ligament assisted by the flexors 

 of the phalanges constitute the inhibitory apparatus. 



It will be noted that provision for weight bearing is so ar- 

 ranged that muscular energy is not required except in the matter 

 of suspension of the body between the scapulae and here tonic 

 impulses only are necessary to maintain an equilibrium^, yet 

 in every instance where weight is not supported by bones, in- 

 elastic ligaments or tendinous structures relieve the musculature 

 of this constant strain. This explains the fact that some horses 

 do not lie in the stall, yet in spite of their constant standing 

 position, they are able to rest and sleep. 



The student of lameness is interested in the function of the 

 legs in the role of supporting weight and as propelling parts, 

 and net ]i;)rtii'ulai'ly in tlic capacity of these members for in- 



^Manual of Veterinary l>hysiolo,a;v liy Major-Oeneral F. Smith, page 580 



