SUPERIOR FACE OF THE BODY. 119 



We believe that the more flexible and elastic the vertebral column 

 is the more it will disperse the effects of concussion from violent 

 exertion or accidents. The back will at any time lose this quality as 

 soon as the alternative efforts which elevate and depress it are enacted 

 in an irregular manner. Let us recall the regular movements of the 

 rope-dancer ; nothing more graceful and of better rhythm. But would 

 they have the same rhythmical character if, for example, he attempted _ 

 to jump without regularity upon his rope? Evidently not ! 



This comparison applies to a certain degree to our subject. In 

 locomotion the weight of the body, whenever it touches its base of 

 support, calls into activity the elasticity of the vertebral column, which 

 describes oscillations whose amplitude is proportional to its elasticity, 

 its degree of tension, and the energy of muscular contraction. If, for 

 one reason or other, these oscillations are excessive, whenever the feet 

 come into contact with the surface upon which the animal moves, an 

 evident antagonism of forces Avill result, leading to a succession of 

 rebounds, which render the reactions still more exaggerated, even more 

 so than if the back had an opposite conformation. Here is, we think, 

 the cause of the divergence of opinions 'which we have spoken of. 



Horses of this type frequently have very feeble reaction when their 

 gait is rhythmical and perfectly regular, as in the ordinary trot or the 

 gallop ; but the reactions become marked as soon as the oscillations of 

 the vertebral column cease to be in accord with the movements of the 

 foot in touching the ground, as in trotting or running at great speed. 



Sometimes the line of the back is oblique from above to below, and 

 behind to before, instead of being horizontal, concave, or convex. Such 

 a form is called dipped. This direction, due to a more or less marked 

 elevation of the croup above the withers, entails an unequal distribution 

 of the body-weight upon the four extremities. The centre of gravity is 

 carried towards the fore limbs, increasing by so much the weight which 

 they support. We shall hereafter have something further to add in 

 respect to the objections which exist with regard to this type of struct- 

 ure when we come to treat of the axial measurements of the body. 



Form. In horses whose muscular system is very highly developed, 

 there exists on the median line of the back a longitudinal line or fur- 

 row, which is slightly surmounted laterally by the environing parts 

 on account of the volume of the muscles situated in the costo-vertebral 

 gutters. This characteristic marks that kind of back which is called 

 double. It is a peculiarity observed in heavy and well-muscled animals 

 whose chest is wide, the back somewhat concave, and the withers low. 

 Many subjects which present it at the time of purchase may not 



