124 



THE EXTERIOR OF THE HORSE. 



Although, from an anatomical and physiological point of view, the croup 

 constitutes the first segment of the abdominal limb, yet, on account of its close 

 relationship with the other parts of the back, we prefer to regard it, for our 

 present purpose, as the terminal portion of the trunk giving attachment to the 

 hind limbs. Solidly united with the vertebral column by bones and muscles, it 



helps to form the periphery of the pelvic 

 cavity. Accordingly, we shall not, in this 

 discussion, separate it from the other regions 

 of the body with which it is so intimately 

 associated. 



Anatomical Base. It has for its 

 base the two coxse, HF (Fig. 34), firmly 

 united on the median line, CD ; anteriorly 

 they articulate with the borders of the sa- 

 crum, S, and are immovable excepting for a 

 certain amount of elasticity. These bones 

 are covered by a large mass of muscles, some 

 of which extend to the femur and to the 

 tibia. On the side is the coxo-femoral 

 articulation, 0, in which the head of the 

 femur takes part, and which supports this region upon the posterior members. 



Considered from a point of view of animal mechanics, the coxa can be repre- 

 sented (Fig. 35) by a bent lever, HOF, composed of two arms : the one anterior, 



HO, formed by the ilium, ex- 

 tending from the external 

 angle of the haunch, If, to 

 the centre of the coxo-femoral 

 articulation, ; the other, 

 OF, formed by the ischium, 

 extends from the centre of 

 the hip-joint to the ischiatic 

 tuberosity or the point of the 

 buttock, F. 



These two bones form a 

 a very obtuse angle, HOF, 

 whose mean extent, as deter- 

 mined by our researches, is 

 from 140 to 145 degrees, but 

 which may vary ten degrees 

 in either direction, accord- 

 ing to the individual. We 

 will call it the ilio-ischlal 

 angle. 



It rests by its summit, 0, 

 upon the head of the femur, 

 at an inclination varying ac- 

 cording to the individual; 



sometimes it is inclined forward, and then the line of direction, HF, tends to be- 

 come more horizontal ; sometimes it tends to an opposite inclination. 



FIG. 35. 



