442 THE EXTERIOR OF THE HORSE. 



the equal distribution of the weight, in order to judge of the soundness 

 of the animal and his locomotory aptitudes. The part of the exterior 

 which includes the study of the axes is therefore full of practical 

 interest. We will treat of them in the following paragraphs. 



Axes, Equilibrium. 



The axes of a horse are nothing else than the direction of the 

 axes of his members in relation to the ground. 



It is necessary, in order to appreciate this direction, to place the 

 subject previously, that is to say, to make him stand in such a manner 

 that the feet of each biped, anterior or posterior, are on a transverse 

 line perpendicular to the axis of the body, and occupy the four angles 

 of the trapezium represented by the base of support. Besides, the 

 plane of the base of support should be perfectly horizontal. 



The axes are called regular when the lines of direction of the 

 members fall perpendicularly and oscillate in planes parallel to the 

 median plane. " The trunk being a weight to be supported/ 7 says M. 

 Sanson, 1 " it is a fact that the members will sustain this weight in a 

 manner all the more efficacious and the more proportionate with the 

 preservation of their integrity, as this same weight is always exerted 

 upon them, in station, in the normal direction of its own gravitation, 

 that is to say, as the different pieces which compose the columns of 

 support are arranged in such a manner that the diverse component 

 forces will be resolved into a single resultant invariably parallel to the 

 plumb-line." 



The axes are styled irregular, on the contrary, when the lines 

 of direction of the members deviate from the vertical and effect other 

 displacements in the planes than those of which we have spoken. 



The line of axis of a member is, theoretically, the vertical line 

 which passes through the point of suspension, that is, the centre of 

 movement of the trunk upon this member. If this vertical line meet 

 the opposite extremity of the locomotory column, here altogether 

 comparable to an ordinary column, it may be supposed that the latter 

 is well placed under the body to fulfil with efficacy its r6le of support. 



On the other hand, it is evident that this condition is dependent 

 upon two principal factors : the length of the osseous segments and 

 the value of their articular angles. The points of origin and of ter- 

 mination of the ideal broken line which represents each member should, 



1 A. Sanson, Nouveau Dictionnaire de mdecine, de chirurgie et d'hygiene veterinaires, t. 

 i. p. 669. 



