LOCOMOTOR SYSTEM 



613 



to a pair of muscles running parallel to each other and function- 

 ing in an opposite sense. 



Chauveau, many years ago, described the tendon of the 

 flexor metatarsi as a conducting cord (Fig. 191, j), the 

 function of which was to regulate the flexion of the hock by 

 purely automatic action. He conceived that this automatic 

 effect was brought about by stifle flexion. There can be no 

 doubt that the position of the cord is greatly altered by flexion 

 of this joint. The more the stifle is flexed, the higher the cord is 

 drawn in the direction of 

 the hip ; and as it is fixed 

 below to the metatarsus, 

 the latter has to follow 

 automatically (Fig. 197). 

 But we cannot concur 

 in thinking that the con- 

 ducting cord can effect 

 flexion without muscular 

 aid, and believe that the 

 flexor metatarsi must take 

 an active share, in spite 

 of the difficulty of ex- 

 plaining precisely how 

 this is effected without 

 inducing antagonistic ac- 

 tion in its neighbour, 

 with which, as we have 

 seen, it possesses a 

 tendon in common. 



The next point to en- 

 gage attention is the 

 astragalus, the hinge-like 

 ridges of which in the 

 horse are arranged ob- 

 liquely, like the threads 

 of a screw. No other 



animal than the horse has oblique ridges to the astragalus. 

 It might appear at first sight that their effect on flexion 

 would be to turn the leg out below the hock. But the 

 horse does not carry his legs in this way. When the hock 

 is flexed, the parts below it are carried forward true to the 

 front ; if the ridges on the astragalus acted on the lower 

 limb, the legs would be flung outwards. The screw of the 

 astragalus affects the joint above and not the limb below it. 

 It turns the stifle outwards, producing the stifle action so much 

 admired in trotting horses. When the hock is flexed, the stifle 



Fig. 199. — Extension Forwards of the 

 Hind-Limb. 



