MUSCULAR ACTION 



393 



true agents of propulsion. Flattening of the arch of the foot is prevented 

 only by the powerful action of the lateral peronei. The posterior 

 femoral muscles, flexors of the supporting leg, begin contracting during 

 the anterior step, and the contraction soon becomes marked and flexes 

 the leg off the ground. 



The previously supporting leg now becomes the swinging leg. At 

 this moment the gastrocnemii and the peronei relax, and at the same 

 time the extensors of the toes and the tibialis anticus contract, the last 

 serving to raise the toes off the ground to prevent their touching it as the 

 leg swings. The flexors of the leg are contracted, but the flexors of 

 the thigh on the pelvis (sartorius, etc.) contract so as to draw forward 

 the thigh and the rest of the leg. Thus the swinging leg advances, but as 

 it passes the vertical the quadriceps femoris shortens v gorously so as to 

 extend the leg from the thigh; this is a quick movement and is quite 

 finished before the advancing leg has stopped. (The swelling seen in 

 the thigh later than this is due to the relaxation rather than to the con- 

 traction of this large mass of muscle) 



The periods of a double-step. The first shows the period of double support, the second the 

 posterior step, the third the moment of verticality, the fourth the anterior step, and the last the 

 period again of double support. (Richer.) 



Other accompanying contractions are to be seen : The spinal muscles 

 contract on the side of the oscillating leg, as does also the deltoid, the 

 anterior and posterior fibers of the latter controlling the natural swinging 

 of the arms. 



The work of Fischer, then, tends to minimize the old passive pendular 

 movement notion of the Weber brothers and to show that it is largely a 

 muscular propulsion. 



In running the phenomena are essentially those of walking, the main 

 difference being in the vigor of the supporting leg's action. All the 

 movements are exaggerated and the supporting leg (gastrocnemius) in 

 extending the foot on the ankle raises the body so strongly that the latter 

 entirely clears the ground and falls, a moment later, considerably fur- 

 ther forward on the far-extending other leg. Running, like walking, is 

 then a system of fallings first on one leg and then on the other. The 

 energy expended is about double (Marey) that of riding a bicycle, but 



