PROPULSION BY THE LIMBS, 



47 



be a fore one. I may remark that a succession of these displacements and 

 recoveries will constitute the walk, run, or other pace. The same movements 





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— ^*JaB=*'"*^ 



Fig. 20. 



Fig. 21. 



Fig, 19, 



DiSPLACEMENr OF CENTRE OF GRWITY BY MAN WHEN WALKING. 



occur when leaping, except w hen the spring is made vertically upwards from 

 a state of jest, in which case the centre of gravity is not displaced beyond 

 the base of suppoit. 



Manner in which Propulsion is Effected by the Limbs,— The 



displacement of the centre of gravity, in the propulsion of the body, is 

 accomplished by the straightening out of the limb or limbs, as the case may 

 be. We can readily see how this gives the required impetus, if we consider 

 the manner in which the shove-off is done by an expert swimmer in a bath, 

 w^hen he comes to the end of it, and wishes to touch, turn, and strike off 

 without loss of time. He, as we all know, will, as much as possible, draw 

 up the leg with which he is going to give the shove off, and having applied 

 it to the side of the bath (Fig. 22), will suddenly straighten it out, with 

 the result that his body will be shot forward (Fig. 23), Here the drawn- 

 up leg, which acts as a spring, is placed between two objects : one (the 

 body) movable, the other (the side of the bath) immovable. When the 

 leg is extended, the movable object is naturally the one to be displaced. 

 Indentically the same action occurs in the various progressive movements ot 

 the horse. We may see it, also, in the run of the pedestrian, which is depicted 

 in Figs. 24, 25 and 26 ; for the right leg, which is a good deal bent in Fig. 24, 

 is nearly straight in Fig. 25, The straightening of the limb or limbs, in 

 effecting the forward propulsion of the body, is even better shown in Figs. 27, 

 28, 29 and 30, which depict the standing leap. 



I may mention that the propulsion of the hind limb of the horse takes 

 place through the hip joint and pelvis. The impetus from the fore leg at the 

 various paces may be regaided as through the elbow jojnt and humerus. 



