THE MEMBERS. 



199 



the descent of the fetlock and the closing of the coxo-femoral and the 

 femoro-tibial angles. 



These articular phenomena are due : to a sudden horizontal direction 

 of the pastern, which pivots upon the os corona, produces a lowering 



FIG. 56. Action of the posterior member in the trot. 

 A. Phase of contact. | S. Phase of elevation. 



of the fetlock, and straightens the canon ; to the forward rotation of 

 the tibia upon the tarsus, which lowers the femoro-tibial articulation ; 

 finally, to a greater obliquity of the femur, which results in a lowering 

 of the coxo-femoral angle. 



2. The development of the impulsive force is effected 

 principally from 2 to 4 (Fig. 56), during which movement the foot is 

 on the ground. In this space the line of direction of the member 

 becomes directed obliquely downward and backward, and the latter 

 becomes elongated progressively by the almost simultaneous opening 

 of all its angles. This takes place first at the pastern, which rotates 

 forward upon the os corona, becomes vertical, and opens the angle of 

 the fetlock ; the canon is now extended and opens the angle of the 

 tarsus; finally, the superior extremity of the tibia is directed more 

 obliquely forward, and the inferior extremity of the femur is carried 

 backward, thus opening the angles of the femoro-tibial and the coxo- 

 femoral articulations. 



The preparation for elevation succeeds the period of impul- 

 sion and manifests itself at 4 (Fig. 56) ; the hoof and the pastern 

 pivot in advance upon the toe, whence a slight flexion of the fetlock : 

 the canon is now rotated backward at its superior extremity, and the 

 movement also produces a feeble closure of the tibio-metatarsal angle. 



