190 THE EXTERIOR OF THE HORSE. 



"We are therefore convinced that during propulsion there is no 

 antagonism of forces, but solely the use of the powers intended to pro- 

 duce an elong-ation of the members according to a definite plan. To 

 become convinced of this, it will be necessary only to examine the 

 muscles of one's own leg, semi-flexed, just before it becomes extended 

 in order to straighten the body ; all the structures are rigid because 

 they all appear to contract in unison, so as to overcome the antagonistic 

 forces. 



On the other hand, mechanical dispositions of great power and the 

 arrana-ements of the muscles and tendons in the hind limbs of the 

 horse associate the articular angles in such a manner that one of them 

 cannot be extended Avithout producing a simultaneous opening of the 

 others. It follows from this that all the forces which are exerted at 

 one point are transmitted at the same time to the adjoining parts and 

 cause them to move successively one upon the other. This process of 

 force-accumulation gives an explanation to some of those spasmodic 

 movements, — string-halt, — so sudden and so energetic, of which the 

 posterior members are the seat. 



Articular Movements ; Orientation or Relative Position 

 of the Angles of Locomotion ; Limited Positions of the 

 Osseous Segments. — The articular movements, being closely 

 subordinate to the extent of the oscillations of the segments which 

 accomplish them, here offer us an opportunity for general considera- 

 tions concerning which we should say a few words. 



It must be admitted, to begin with, that amplitude of joint-action 

 must increase in a ratio with the initial displacement of the bony levers 

 as studied in their condition of rest when compared with the line of 

 their regular axis. 



But the effectiveness of this play depends upon another considera- 

 tion of primary importance. It is indispensable that the line of direc- 

 tion of the segments of the member should hold certain determinate 

 relations with the vertical line passing through their centre of move- 

 ment. In other words, it suffices not that the articular angle which 

 they form be well opened, but it is also necessary that the angle be 

 well located for progression. This condition is realized whenever the 

 angular displacement of the branches of an angle of locomotion tends 

 to separate the two extremities of the member to which it belongs, fol- 

 lowing a very oblique line rather than the vertical or some analogous 

 direction. When such a relation does not exist, the locomotory 

 columns passing over too little surface at each step, are not properly 

 extended in a forward movement, but are merely elevated, and the 



