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of the rectus femoris muscle, which binds down the patellae, straps up 

 the heel, and brings the whole machine into harmony at the moment 

 that the spring is about to take place. 



The admirable mechanical economy of the leg of the ostrich may be 

 illustrated by the parallel case of the Cornish pumping engine. Let us 

 suppose a 100-inch cylinder engine about to commence its downward 

 stroke, and to lift the pump rods, weighing many tons, by means of a 

 force of steam which commences at a maximum, and is gradually let off 

 by expansion to a safe and manageable quantity. It has been found by 

 experience that it is necessary to cause a minute vibration of the beam 

 before letting on the full force of the steam — such vibration shaking all 

 the nuts and pins into their proper positions before the great and 

 sudden action of all the parts takes place ; and if such a precaution were 

 to be omitted, it is well known that the sudden impulse of the steam 

 would break the engine. 



In the leg of the ostrich, the M. rectus femoris supplies the place of 

 the preliminary vibration ; it acts before the extensor muscles come into 

 full play; it binds down the two patellae, braces up the heel joint, and 

 gives the signal for the M. gastrocnemido-solceus and other associated 

 muscles to contract, and thus produces what may be regarded as one of 

 the most striking phenomena in nature, viz., that the delicate bones and 

 ligaments of a bird- s leg, acted on by muscles equal to those influencing 

 the hind leg of a horse, shall remain uninjured under the sudden 

 action of forces, the slightest error in the application of which would 

 break to pieces the machine on which they act. 



I can admire, though I do not envy, the reasoning powers of those 

 Naturalists who believe that a mechanism such as this grew out of pre- 

 existing forms without the interposition of an intelligent mind ; and 

 for myself I must declare, that I could as easily believe that the modem 

 Cornish engine had developed itself from its clumsy predecessors by the 

 way of Natural Law, and without the interposition of intelligent engi- 

 neers, as that the leg of the Ostrich was produced by Natural Selection 

 from the commonplace legs of its less perfect ancestors. 



