Principles Underlying the Draft of the Horse. 495 



With the spring balance represented above the back of 

 the model in Fig. 235, which controls the hinged hock 

 joint through a rod, it is possible to vary the tension which 

 holds it rigid and thus demonstrate the ratio of muscular 

 tension to the draft on the load and show that with too 

 weak muscles only a portion of the weight of the body can 

 be utilized in draft. In the model the tension of the hock 

 muscle is about double the draft and while this is not in- 

 tended to demonstrate the relation of strength of muscle 

 to intensity of draft in any horse it illustrates the funda- 

 mental principle and shows how extremely powerful the 

 muscles of the horse must be to permit him to make the 

 draft he does. 



618. Influence of the Width of the Hock on the Draft of 

 the Horse. Not less important than the strength of the 

 hock muscle, in determining the qualities of a draft ani- 

 mal, is the "width of the hock joint" itself; or, stated in 

 the language of mechanics, the ratio between the two arms 

 of the lever upon which the hock muscle acts. If the pro- 

 jection of the heel bone backward, which forms the point 

 of the hock, is long in comparison with the distance to tho 

 hoof, as represented in the diagram, Fig. 236, at the left, 

 instead of short n ^hown at the right, then it is clo-ir that 



FlQ. 240. LM.ia'ram .-U.JVM.I^ .liJoicuce botwee.j wide aud narrow iioci* 



with a given strength of hock muscle it will be possible to 

 straighten the limb under a greater pull and the ability of 

 the horse to draw is thereby increased. In the model rep- 



