92 MUSCULAE SYSTEM, 



would be necessary to project the arrow as far, if 

 applied directly. One miglit suppose that though the 

 force required to pull the spring forward might be 

 much less than that necessary to move it backwards, 

 still, as the spring is habitually carried with the points 

 forward, there would be a constant strain in the one 

 case, and only an occasional effort wanted in the 

 other. 



When, however, the spring points straight forwards, 

 there is perhaps little strain on it ; moreover, there is 

 a httle catch (Pis. LVII x, LVIII, fig. e), which 

 is an organ homologous with the spring itself, but situ- 

 ated on one of the anterior segments; this passes 

 between the two arms of the spring, and keeps them in 

 place. It answers in fact to the catch in a crossbow, 

 and as soon as it is drawn forwards, the muscle pulls 

 the spring downwards, and its own elasticity does the 

 rest. 



A joriori it might have been supposed that a position 

 of rest was one of relaxation, in which the muscles 

 were, so to say, at ease, but ready to spring up to 

 attention in a moment if necessary. On the contrary, 

 however, we find very often that a position of rest is a 

 state of opposite tensions. 



Take, for instance, our own case. The upright 

 position which seems so easy and natural to man, is, 

 says Prof. Huxley, in his excellent lessons in elemen- 

 tary physiology, " the result of the contraction of a 

 multitude of muscles which oppose and balance one 

 another. Thus, the foot affordiug the surface of sup- 

 port, the muscles of the calf must contract, or the legs 

 and body would fall forward. But this action tends to 

 bend the leg ; and, to neutralize this and keep the leg 

 straight, the great muscles in front of the thigh must 

 come into play. But these, by the same action, tend 

 to bend the body forward on the legs ; and if the body 

 is to be kept straight, they must be neutralized by the 

 action of the muscles of the buttocks and of the 

 back." 



