240 THE EXTERIOR OF THE HORSE. 



the slow draught-horse may be more accentuated, since the coxa is 

 less horizontal, but this modification is rarely observed. Ordinarily, in 

 these horses, the femur is straighter at the same time that the croup is 

 slanting, which thus increases this angle instead of diminishing it, so 

 as to place the inferior parts of the member in a less defective position 

 in relation with the vertical axis. 



Examinations of instantaneous photographs teach us that the 

 limit of extension of the crural segment is situated but slightly pos- 

 terior to the vertical line passing through the centre of the coxo-femoral 

 articulation. 



In principle, therefore, the thigh should not be too sti-aight when 

 the animal is normally at rest, — that is to say, when the line of direc- 

 tion of the femur becomes confounded with the vertical line which 

 extends from the centre of suspension of the limb upon the trunk. 

 (See Vertical Axes.) 



When it is thus (Fig. 72, AB), the degree of extension of the 

 femur is necessarily limited, the animal lacks action, and is incapable 

 of utilizing the advantages of a long croup. Besides, his vertical axis 

 becomes vicious, and the hock and the foot carried too far backward, 

 render him camped behind. As to the muscles, the gluteals, HA, the 

 extensors of the leg, mn, and the ischio-tibial muscles, Go, are short ; 

 the flexors, iH, alone are long. 



When the femur, on the contrary, is too oblique, as CD, it is the 

 flexion th^t is unduly limited. The arc which the foot describes at 

 each step is too short ; the member, stationed too much under the trunk, 

 works upward, and loses a part of its extension power in raising the 

 body instead of projecting it forward, whatever may be the greater 

 length of the gluteal muscles, HC, of the ischio-tibials. Go", and the 

 extensors of the leg, mn". 



On the other hand, the degree of inclination of the thigh being 

 capable of modifying the value of the coxo-femoral angle, it may be 

 questioned whether, for velocity, the obliquity of the croup would not 

 be capable of compensating the excess of obliquity of the crural seg- 

 ment in such a manner as to leave to this angle the same opening and, 

 consequently, the same degree of pla\'. 



This compensation, as we have seen above, is possible, but only 

 within very narrow limits, because the orientation of the articular 

 angle soon becomes defective ; its bisecting plane assumes too horizontal 

 a direction. Here, as in the arm, the principle is : to a horizontal 

 croup should correspond a straight thigh. 



On the other hand, if it be necessary that the femur should pre- 



