476 THE EXTERIOR OF THE HORSE. 



that is to say, the distance DD f , equal to the distance described by one 

 of t^ie feet, the distance comprised between two attitudes, HD and 

 H"D', identical and successive in this member. (See Generalities of 

 the Members, page 194.) 



The length of the step is therefore measured by the distance 

 separating the two points of contact, DI) f , successive of the same foot. 

 If the axis is regular, the vertical line which passes through the centre 

 of suspension or of oscillation of the member necessarily divides this 

 intervening distance into two equal parts, each one equivalent to a 

 semi-step. 



Finally, we have also seen that the two principal phases, contact 

 and elevation, insufficient for the needs of an exhaustive analysis, 

 must be subdivided into equal secondary phases, called periods, six in 

 number, as follows : 



( 1st period, from to 1, commencement of the contact. 

 Phase of contact with soil. \ 2d period, from 1 to 2, middle of the contact. 

 ( 3d period, from 2 to 3, end of the contact. 



!4th period, from 3 to 4, raising. 

 5th period, from 4 to 5, middle of elevation. 

 6th period, from 5 to 6, rest. 



Periods of Exchange of Contact. If, after the example of 

 M. Lenoble du Teil, we study more attentively the evolution of the 

 members of the same biped, anterior or posterior, during the marched 

 gaits, we notice two moments when the weight of the body passes 

 from one foot to the other, and vice versa. 



Thus (Fig. 172), when the posterior right foot is placed on the 

 ground, the left is not being lifted, as might be believed, but is really 



at the end of its period of con- 

 tact; in the same way, it is only 

 when the right foot commences 

 its contact that its congener rises. 

 In other words, in these gaits the 

 commencement of the contact of 

 one member does not wait until 

 that of the other has been com- 

 ^'^r^^^l~ i^y*^""** pleted ; it precedes the latter a 



FIG. 172. Exchange of contact upon the posterior short time. But for this the 



bipeds in, he *. j^ ^^ haye m) 



(From an instantaneous photograph.) 



during the interval between the 



successive movements. The consequence of this fact is that the dura- 

 tion of the contact of the foot with the ground is always longer than 

 that of its elevation, contrary to the opinions of Vincent and Goiffon, 



