SUPERIOR FACE OF THE BODY. 129 



the thickness "of the croup, is, therefore, in relation with the length of 

 the muscles, the extent of rotation of the coxae, and, consequently, the 

 aptitude for galloping and leaping. This straightness may at the same 

 time be considered, in horses of rapid movement, as an index of great 

 power and strength in the upper part of the hind quarter. 



Width. The width is the distance between the external angles 

 of the ilia, but depends also upon the separation of the points-of the 

 buttock. 



In the skeleton, the interval between the external angles of the ilia 

 always slightly exceeds the length of the ilio-ischial line ; in other 

 words, the pelvis is wider than long, the excess varying from two to 

 seven centimetres, according to our measurements. 



In the living animal it is otherwise on account of the thickness of 

 the muscles which cover the ischiatic tuberosity ; the length of the 

 croup becomes equal to, and sometimes exceeds, its width in heavy 

 horses from two to five centimetres. 



The development of the transverse diameter of the region varies 

 evidently with the race and the conformation of the animal, but is, in 

 general, an index of the volume of the muscles, and, consequently, of 

 their contractile power, the fibres or contractile units being more 

 numerous in a wide croup than in any other. Such a croup is, there- 

 fore, an absolute beauty, and a most desirable feature in a horse, 

 no matter for what service he is intended ; but it is especially desirable 

 in horses used for heavy work, in which the greatest possible effort is 

 exacted. It is even more desirable in broodmares. 



The separation of the haunches is far from furnishing, though it 

 be so regarded, the best criterion for judging of the true width of the 

 croup. Horses having an equal measurement over the haunches may 

 have, in reality, ilia very different in their transverse diameter. It is 

 not rare to meet some subjects whose haunches are less separated than 

 most others, but whose pelvic measurements and iliac surfaces are con- 

 siderably larger. 



We have convinced ourselves that these individual differences 

 depend upon the following causes : 



1st. The degree of inclination of the iliac surfaces from above to 

 below. 2d. The degree of concavity of the external iliac fossae. 



The first cause effects a lowering of the external angle of the ilium 

 in relation with the summit of the croup, and brings it towards the 

 median plane of the body, a circumstance which, it is true, diminishes 

 the distance between the haunches, but which exercises no influence in 

 any manner upon the peripheral surface of the bone for muscular attach- 



9 



