3- The tibia closes toward horizontality and its move- 

 ment has a width of 40°. The femoro-tibial angle closes 

 about 20°. It therefore does not assist in propulsion. 

 Its role is to be a shock absorber, at least, during positions 

 o, I and 2. 



The stifle is lowered during the whole period (even 

 when the pastern straightens up). It is this peculiarity 

 which permits the femur to straighten up without having 

 to raise the weight of a part of the hind quarter. The 

 coxo-femoral joint slides, so to speak, softly upon an in- 

 clined plane. The very weight of the hind quarter as- 

 sists the production of this motion. 



4. The metatarsus moves toward verticality. 



The tibio-metatarsal angle begins by opening slightly 

 to the extent of 4° between positions o and i, then it 

 closes by 10° between positions i and 2, and finally opens 

 quickly by 24° at position 3. 



These variations must be interpreted. 



In spite of the opening of the tibio-metatarsal angle 

 between position o and position i, contrary to what one 

 may, and have, supposed, there is no propulsion. 



The metatarsus straightens up more quickly (16°), 

 then the tibia bends, and this rapidity is because the 

 lower extremity of the metatarsus (the fetlock joint), in 

 consequence of the bending of the pastern, is carried be- 

 hind the position which it occupied at position o. Hence, 

 opening of the tibio-metatarsal angle, but there is no ques- 

 tion of impulse since the phalangian lever which acts as 

 a base for the metatarsus is in the act of bending, and 

 could not give them a sufficiently solid support to make 

 an effort useful in propulsion. 



The above explanation becomes evident if one con- 

 siders what takes place between position i and position 2 

 when the tibio-metatarsal angle closes by 10°. It is very 

 certain that it plays, up to that time, at the level of the 



40 



