ANIMAL LOCOMOTION. 



59 



(Fig. 1). The ilio-psoas would have an apparent effect in prevent- 

 ing this. It may be surmised that this muscle is a check to the ex- 

 cessive inward rotation, or the muscle may not contract until later, 

 and prove to be the chief factor in the second stage of the recover. 



(See p. 89.) 



Fig. 1. 



The figure is designed to illustrate the disposition for tlie limb to i-otate inward. The inner border 

 of the uplifted foot ia oblique, and the leg is inclined towards the median line of the body. 



THE GAIT, OR THE SUCCESSIONS OF FOOT-FALLS. 



The order in which the feet comes to the ground would be a 

 simple matter for study if the animal moved constantly at a given 

 speed and gait. It is rational to assume that the movements are 

 in part automatic, and the alternate motions of the right and left 

 limbs, or the motions of both the left limbs alternately with both 

 the right limbs, would insure a succession which could be premised. 



Motions are as a rule rhythmical. One expects the serpent to 

 undulate the trunk after a regular method, no matter what the 

 speed of the animal may be. In flying and swimming, so far as 

 is known, the movements are synchronous and constant. 



In the terrestrial movements of the quadruped, however, such 

 is far from being the case. This is owing to a variety of causes. 



