ANIMAL LOCOMOTION. 57 



the forward strain is the greater. In the fawn, as already re- 

 marked, the feet are more flexed than in the adult deer. An 

 untrained adult feral animal is, all things remaining the same, 

 the best form which should be taken for study. 



The weight of the rider being thrown forward on the fore legs 

 may modify the gait. That the depression of the head in the 

 forward movement of the legs is not dependent upon this circum- 

 stance is shown in the figures of the rocking horse (series 649 A). 

 An additional reason is here presented why, when practicable, a 

 form taken for study should be feral. (See also remarks on the 

 trot, p. 66.) 



Torsion of the Trunk. 



An animal in thrusting out a limb from the body may be com- 

 pared to a boxer making a thrust with his arm. With each lunge 

 the body is turned in the direction in which the lunge is made, and 

 the impetus of the body-movement is added to the force of the 

 blow. The twist that the body describes is checked by the plant- 

 ing down of one of the disengaged feet. 



In the dog (series 707), Avhile both hind limbs are off the ground 

 and the body is being vaulted on the single fore limb, the entire 

 posterior part of the body is deflected from the line of the main 

 axis of the vertebral column. This motion is certainly dependent 

 on the bending of the column, and is probably an example of 

 torsion. If unchecked the motion would " twirl" the body round 

 on itself. 



But since the impression of the foot on the ground remains 

 sharply outlined, it is probable that the "twirl" is greater in the 

 proximal than in the distal joints, and is entirely lost by the time 

 that the parts of the limb are reached which rest upon the ground. 

 Thus the first impetus towards deflection, while originating in the 

 vertebral column, is gradually transferred to that limb which at 

 the time is serving as a prop, and the force of the movement is 

 dissipated as the animal is carried forward. 



In animals possessing a rigid vertebral column the torsion 

 which corresponds to the movement above described is not 

 marked. But the disposition of the body to incline towards the 

 side which perfects the forward strain — i.e., delivers the blow — is 

 the same. Such inclination if unchecked would throw the body 



