126 



THE EXTERIOR OF THE HORSE. 



gluteal region, the principal extensors of the femur. They, in con- 

 nection with the other extensors of the hind limb, communicate to the 

 body a greater impulse, which carries it forward by a sudden and 

 forcible opening of all the locomotory angles and a straightening of 

 the whole limb. The greater their length the more they will be capable 

 of shortening during contraction, and, consequently, the greater will be 

 the force which the hind limb possesses. 



This impulsion, besides, will have greater power, because the inser- 

 tion of the muscles will have an incidence approaching the perpendicu- 

 lar. The line CD', which represents the direction (Fig. 36), is less 

 oblique to BC {or CO) than the line CD. 



Again, the length of the croup is concomitant with that of the 

 ischio-tibial muscles, AB and A'B, which flex the tibia or rotate the 

 coxse backward during rearing or progressive movements in which they 



Fig. 36. 



Fig. 37. 



are concerned, as the gallop or leaping. Not only the length but the 

 angle of incidence is also modified. 



This is not all. It is also instructive to inform ourselves as to how 

 the length of the croup is produced, for there are three principal fac- 

 tors which enter into its formation, — 1st, the degree of openness of the 

 ilio-ischial angle ; 2d, the length of the ilium ; and, 3d, the length of the 

 ischium. 



The openness of the ilio-ischial angle, according as it is more or 

 less large, separates correspondingly the angle of the haunch from the 



