hock, the same shock absorbing role as the femoro- 

 tibial angle at the other end of the tibia plays at the level 

 of the stifle. 



But between positions 2 and 3 (and probably nearer 

 to position 3 when the phalanges becomes vertical), the 

 tibio-metatarsal angle, opens quickly by 24°, and ener- 

 getic propulsion is produced. 



Thus the tibio-metatarsal angle changes from the shock 

 absorbing role which it has during the first part of the 

 period of support, to the role of propulsion to the second 

 part. 



5. The phalangian lever begins by moving toward hori- 

 zontality during the first part of the period of support and 

 rises toward verticality during the second part; the 

 metatarso-phalangian angle follows the same variations, 

 beginning by closing and then opening, assisting first 

 shock absorption, and then propulsion. 



The radii which become erect, the femur during the 

 whole period of support, the metatarsus and the pha- 

 langian lever during the second part of this period, are 

 the only ones which contribute to the total stretching of 

 the leg, and consequently are the only ones w^hich par- 

 ticipate in propulsion. It will seem advantageous for 

 propulsion, therefore, to lengthen these radii. 



So far as the femur is concerned, this is doubtless so. 

 This radius acts as a lever for the extrinsic muscles (the 

 rump muscles, the ischio-femorals and the ischio-tibials), 

 which produce propulsion from the very beginning of the 

 period of support ; its great length which implies great 

 length of the ischio-femorals and ischio-tibials is emi- 

 nently favorable to power of propulsion. 



The case of the metatarsus is not the same : the twin 

 muscles which act at the top of the hock make of this 

 radius an inter-resisting lever in which the difference be- 

 tween the lever arm of force and that of resistance 

 (length of the cancaneum) remains constant when the 



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