132 



THE EXTERIOR OF THE HORSE. 



1st. Variations in the Inclination of the Ilium. — When the Ilium approaches the 

 vertical (Fig. 38), the croup A'B is more oblique and shorter than the croup AB. 

 The length of the gluteal muscles A^'C is diminished; nevertheless, this 

 incidence is more favorable than that of AC, whether for the extension of the 

 femur or the support of the vertebral column. The advantages which follow 

 from this incidence are more efficacious than is generally believed. Are they not 

 evident in the draught-horse, for example, when he endeavors to move his load ? 

 The effort inclines his croup and closes proportionally his articular angles, which 

 otherwise are more open. Is it not the immediate consequence of this variation 

 to augment the intensity of the muscular contraction, by rendering the insertion 

 more perpendicular to the bony levers on which they act? If, therefore, from this 

 circumstance the animal approaches a conformation which saves him from exerting 



all his efforts during traction, he will realize 

 a certain economy of force which must not 

 be overlooked. 



The coxo-femoral angle, A^OD, being 

 very obtuse, the weight of the body will 

 distribute itself more perpendicularly upon 

 the bones; the muscles A^C and BE, 

 charged to support the spinal column, 

 will expend less force. 



From an opposite point of view, if the 

 coxo-femoral angle, A'OD, become more 

 obtuse, it places thQ femur in a position 

 much closer to its limit of extension. (See 

 Grneralifies of the Members.) It follows, 

 then, that if the coxa, by its uprightness, 

 increase the dimension of the angle J''OZ>, 

 which is already large, this bone can only 

 pass through a lirnited distance during the 

 act of extension, because at the moment of 

 the propulsion of the trunk the posterior 

 limit of the femoral play is reached much 

 more quickly. The movements of the femur 

 will, on the contrary, be much more extensive with the angle AOD less obtuse 

 and approaching the ilium towards the horizontal direction. 



If the ilium be lowered, the results are precisely of an opposite order. We 

 will, therefore, not pass fi^rther into details. 



The following conclusions are derived from the study of this 

 mechanism (Fig. 38) : 



With the obUque ilium, the gluteal muscles are shorter, but better 

 inserted for intensity of power ; the fixation of the spine is more easy ; 

 the movements of extension and flexion lack amplitude ; and the 

 impulsion is transmitted more vertically. Force is increased and speed 

 is diminished. 



With the ilium /(oy/.-;o/(to/(that is to say, less upright), the mechanical 

 conditions are the opposite of the preceding ; the muscles are long ; the 



