I. The hip moves toward horizontaHty during the 

 whole period of support; it changes by almost 20°, but 

 these variations of slope do not come from a motion 

 peculiar to the hip itself. Firmly fixed to the sacral 

 vertebrae, the hip is susceptible of no rotation and 

 its changes of slope are only the measure of the play of 

 the lumbar arch, which, set like a bow during the pe- 

 riod of suspension, springs and straightens out during 

 the period of support. This very important action of 

 the lumber arch is productive of impulse and effectively 

 helps the lightness and power of the gallop. But it is 

 well known that the opening of an angle means the pro- 

 duction of impulsive effort. In the species under con- 

 sideration, it is a question of the imaginary angle ABC 



Fig. 6. 



(Fig. 6) formed by the intersection of the two tangents 

 A B and B C to the double curvature of the loins. When 

 the angle ABC opens, the line A B (which corresponds 

 practically with the direction of the ilium) moves toward 

 horizontaHty. It is this which explains why the move- 

 ment of the hip toward horizontaHty has no shock ab- 

 sorbing effect, but it is the result of the production of 

 force. From this remark can be drawn the immediate 

 conclusion that one should not seek too short a loin in a 

 powerful animal : 



2. The femur rises toward verticality with a constant 

 movement and the coxo-femoral angle opens, hence pro- 

 pulsion. 



39 



