748 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



from the two rapid sounds when the feet of the opposite side strike the 

 ground. 



It has been seen that in the movement of locomotion in man there 

 are two periods of time in which both feet are on the ground and only 

 one interval in which only one foot is in contact with the earth. In 

 running, on the other hand, there is a moment in which one of the legs 

 is raised up while the other is still performing the pendulum motion, and, 

 consequently, both legs are at one time in the air. This interval is, how- 

 ever, much shorter than that in which both feet are on the ground. 



(c) The Trot. The form of locomotion seen in the horse and more 

 seldom in the ox and other quadrupeds which corresponds to the act of 

 running in man is termed the trot, in which the fore leg completes its 

 movement with the diagonal hind leg ; so that in the trot the diagonal feet 

 and hind limbs at the same moment leave the ground and at the same 



FIG. 309. THE TROT. (Colin.) 



moment again reach it. Therefore, in the trot two strokes of the feet 

 on the ground are heard at each step. In the fast trot an interval occurs 

 between this double stroke of the feet against the ground in which the 

 body is moving through the air with all four feet raised from the ground. 

 This interval is variable, usually being about half the time that the 

 feet are in contact with the ground. 



In the trot the impulse is communicated to the pelvis from each hind 

 leg alternately, so tending to strain the articulation between the sacrum 

 and vertebrae. This is, however, reduced to a minimum by the contrac- 

 tion of the ilio-spinalis of the opposite side. 



In a very fast trot the second pair of feet leave the ground as soon 

 as the first pair have reached the vertical position. Each step in the trot 

 is twice as long as the step in the walk, in rapid trotting the hind feet 



