128 THE EXTERIOR OF THE HORSE. 



Here are some very suggestive figures which show these dimensions relatively 

 in certain species other than the horse : We have found the relation to be 0.57 in 

 the swan ; 0.87 in the turkey ; 1.22 in the hare and the rabbit; 1.30 in the lion ; 

 1.50 in the cat ; 1.60 in the greyhound ; 1.56 in the goat. In the ox it is only 1.24 : 

 it is smaller than in the horse. 



t 



In all animals in which the anterior part of the body has no direct 

 support, as in birds, or is comparatively heavy, as in the larger rumi- 

 nants, or, again, when the natural mode of progression is galloping or 

 leaping, the ratio diminishes in consequence of the relative increase of 

 the ischium. 



The result is apparent. It is easy to determine the proportions of 

 the two levers constituting the coxa, by the distance comprised between 

 the centre of the articulation and the point of the buttock. This factor 

 is at least useful, if not indispensable, in estimating the locomotory apti- 

 tude of the animal. 



To recapitulate : the length of the croup is in close relation with 

 the production of speed. The ilio-ischial line is an insufficient indica- 

 tion, and often the source of error. We should primarily strive to 

 estimate the length of the bones which constitute that line, and should 

 attach only a secondary importance to the line of direction ; or, in other 

 words, to the openness of the angle which they form. 



Thickness. — Authors have said but little upon the thickness 

 of the croup, a point which should, nevertheless, be taken into con- 

 sideration. We may define it as the distance comprised between the 

 antero-posterior axis of the cox^ and the summit of the sacral spine. 



The interval between the sacrum and the coxae is greater at the 

 outlet than at the inlet of the pelvic cavity, on account of the inclina- 

 tion of the axis of the croup and the horizontal tendency of the axis 

 of the sacrum. It varies singularly in different subjects, owing to the 

 peculiarities of the form of the sacral spine and the general direction 

 of the sacrum itself. This bone may often be curved in draught-horses, 

 while it is ordinarily more or less rectilinear in animals possessed of 

 speed, notably the English thoroughbred and his descendants. The 

 more it is depressed the smaller will be the coxo-sacral interval, or the 

 less the thickness of the croup. 



When it is straight, on the contrary, this interval augments, and the 

 line which marks the profile of the croup contrasts more strongly with 

 the ilio-ischial line. The region then appears horizontal. 



Numerous muscles, among them the ischio-tibial muscles, charged 



• with the rotation of the pelvis and the fixation of the spinal column, 



attach to the sides of the sacral spine. Its straightness, also indicating 



