CHAP. I.] THE SCREW TREAD, HOW ACQUIRED. 31 



because the resistance to be overcome is then 

 greatest, and we can thus form an opinion how 

 much " he has the free use of his legs." When 

 this is the case, all horses step short ; but, upon 

 even ground, the hind leg, to be perfect, should 

 come firmly forward in the walk, and occupy the 

 identical spot which the fore leg had just quitted. 

 See further at Section 8. As the horse gets old, is 

 tired, disordered, or over-much laden, he ceases to 

 do this as usual, in the exact ratio that he is affected 

 the one way or the other. 



When age overtakes an animal, we may rest 

 assured some of the evils of a too long life attend 

 it. The heavy work which the horses we have now 

 chiefly in view, are put to, strains every joint, of 

 the hind legs principally ; as high as the setting on 

 of the leg to the pelvis, [I. 35.] or the juncture of 

 this bone with the last vertebra of the back, [E. 31.] 

 and even the back bone itself, this species of ruin 

 works its way with years, upon fine, strong and ro- 

 bust horses, as much or more than any other. Then 

 it is the hind leg comes forward much farther in 

 the walk than in early life, and it acquires a twist 

 or screw, which is denoted by a screwing, markedly, 

 upon the ground, and visible all the way up in 

 bad cases. Speedy horses have the same screw 

 in going, though not so apparent, when the limb is 

 similarly strained ; but in some cases great aridity 

 of muscle, the effect of hard work and want of 

 care, amends trivial strains, whilst the tread also 

 becomes shorter. 



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