8 



STRUCTURE AND FUNCTION 



The stability of equilibrium is in direct proportion to the 

 size and especially the width of the base of support. It is the 

 measure of jWAver. Power and speed are not correlated but oppo- 

 site extremes. Instability of equilibrium is the measure of 

 speed. In order, therefore, that the horse may take strides in 

 rapid succession, the base of sup2:)ort must be so reduced as to 

 permit of the ready displacement of the centre of gravity. It 

 may then readily follow^ the direction of each stride in turn. 



Increase in the rapidity 

 of the stride has the 

 effect of reducing the 

 size of the base of sup- 

 port, so that the faster 

 a horse goes the more 

 favorable are the condi- 

 tions for still greater 

 speed. This is exempli- 

 fied in the fact that the 

 base of sujiport is a rec- 

 tangle in case of the 

 hoi*se at rest(Fig.5). It 

 is reduced to the general 

 form of a triangle as the 

 horse leads out with one foot at the walk. It takes tiie form of a 

 line as the horse extends himself at tlie trot or pace ; and finally 

 it consists of a point only as but one foot is on the ground at the 

 run. On the other hand, the horse at the run is not capable of 

 any draft effort except that w^hich comes from the momentum 

 he has already attained; he has a better chance at the trot; can 

 pull well at the walk, and he is capable of his greatest effort at 

 the starting of the load, as he is practically standing on all fours 

 (Fig. 6). 



j^. ^ REVIEW 



1. Of what does the horse's mechanical structure consist ? 



2. How is locomotion accompHshed? 



3. What constitutes a stride and what are its phases'? 



4. Explain the part played by the muscles in locomotion. 



5. Where is the centre of gravity in the horse standing naturally? 



Fig. 6. — During the greatest effort the base of 

 support is rectangular, the horse being practicallj' on 

 all fours. 



