272 On the Muscular Mechanism of the Leg of the Ostrich. 



ten times the force employed in restoring the legs of the animal 

 preparatory to its next spring — more exactly, as 335*5 to 33*75. 

 This enormous force acts on bony supports which are required, 

 by the necessities of a bird's existence, to be as delicate and 

 light as possible; and it is, moreover, exerted almost instanta- 

 neously, so as to give the fullest effect to the bird's spring. 

 The question naturally arises, How is this force to be suddenly 

 applied, without breaking or dislocating the animal's leg? 



The answer to this question is to be found in the peculiar 

 structure 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 pum ping- 

 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 com- 

 mences at a maximum and is gradually let off by expansion to 

 a safe and manageable quantity. It has been found by experi- 

 ence 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 rectus femoris muscle supplies 

 the place of the preliminary vibration ; it acts before the extensor 

 muscles come into full play; it binds down the two patella?, 

 braces up the heel-joint, and gives the signal for the gastrocnc- 

 mido-solseus 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 liga- 

 ments of a bird's leg, acted on by muscles equal to those influ- 

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

 the sudden action of forces the slightest error in the appli- 

 cation 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 can believe that a mechanism such as this 

 grew out of preexisting forms, without the direct interposition of 

 an Intelligent Mind ; and for myself I must declare that I could 

 as easily believe that the modern Cornish engine had developed 

 itself from its clumsy predecessors by the way of Natural Law, 

 and without the interposition of intelligent engineers, as that 

 the leg of the Ostrich was produced by Natural Selection from 

 the common-place legs of its less perfect ancestors. 



