288 THE ARTISTIC ANATOMY OF ANIMALS 



The second shows what takes place during the ascent of 

 a staircase. At a certain moment, the weight of the body is 

 upon both feet at the same time, one of them not quitting 

 the lower step, until the other is already in contact with 

 the step above. Accordingly, there is thus produced an 

 overriding of the pressures. 



The third is relative to running, and has already been 

 represented in Fig. ii8. The pressures of the feet are 

 separated by the times of suspension. 



The fourth also represents running, but in this case 

 more rapid and characterized by the shorter pressures, 

 the slightly longer periods of suspension intervals, and the 

 quicker succession of movements. 



Before putting aside the indications relating to the 

 walking movements of man — indications which it was neces- 

 sary to give in order to render intelligible those which are 

 connected with the paces of the horse — we have yet to fix the 

 value of that which we call ' a step.' 



It is generally admitted that a step is constituted by the 

 series of movements which are produced between the corre- 

 sponding phases of the action of one foot and that of the 

 other — for example, between the moment at which the 

 right foot commences its pressure on the ground and that 

 at which the left foot commences its own. It is necessary 

 to adopt here another method of looking at it, and to 

 regard the preceding as being but a half -step. The step 

 should then be defined as being constituted by the series 

 of movements which are executed between two similar 

 positions of the same foot — as, for example, between the 

 commencement of a pressure of the right foot and the 

 similar phase of the following pressure of the same foot. 

 We shall soon understand the importance of this definition. 



Before entering on the details of the paces of the horse, 

 it is necessary to see how the limbs of the latter oscillate 

 during the period of a complete step ; or, which is the 

 same thing, to determine what the displacements are which 

 a limb executes between two similar positions of its foot. 



If we examine one of the limbs during a forward move- 

 ment of the animal, we see that this limb passes through 



