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working along an imaginary line, passing from the same point in the 

 tiger from which it passes in my pelvis to the very same point, the top 

 of the fibula, to which it is attached in my leg also. Here Nature is not 

 to be accused of departing from the principle of least work. In this 

 case, the strict carrying out of that principle would injure her in other 

 ways, as in the packing of the muscles ; therefore she has deliberately 

 abandoned it, making a small sacrifice in order to obtain a greater 

 advantage. Nature always acts upon the French proverb, " Reculer 

 pour mieux sauter." I have said before that she is at perfect liberty to 

 use, as far as I am concerned, either the penniform or the prismatic 

 muscle; and I cannot criticise her proceedings in that respect. Still 

 her use of the penniform muscle is very sparing, as if she did not like 

 to use her resources except when they were absolutely necessary. We 

 find, although there is no loss of force in a penniform muscle, it is 

 a rare form of muscle, and only resorted to when there is a worthy 

 object. The most remarkable example I can give you of the penni- 

 form muscle in Nature is the muscle which lifts the wing of the bird. 

 The bird's wing is depressed by great and powerful muscles, which I 

 shall describe at the close of the lecture : it is lifted by a small compact 

 muscle, which is placed upon the breast of the bird, in order to keep 

 the centre of gravity of the bird as far back as possible. It is worthy 

 of remark, that in the case of the ostrich, which does not fly, Nature 

 places this muscle on the neck of the bird, because it is no injury to the 

 ostrich to have the muscle on the neck ; whereas it would be destruction 

 to any other bird to have it so. This muscle placed upon the breast works 

 by a tendon passing through a pulley, and changes through an angle of 

 I So degrees in its application, so as to lift the wing of the bird. The 

 nature of a bird's flight is this : The depressor muscles of the wing must 

 be made enormously great, to strike the air with the utmost force ; the 

 muscles which lift the wing must be made as light and small as possible, 

 because their only object is to bring back the wing through the air after 

 the stroke is made ; this ought to be done in the shortest possible time, 

 because, while the wing of the bird is rising through the air, the bird is 

 falling : therefore we find that Nature, or rather the great Author of 

 Nature, always employs the penniform muscle to lift a bird's wing ; and 

 for this reason, since the fibres converge at an angle towards each other, 

 by compounding their forces the velocity along the diagonal is greater 

 than it would be in a prismatic muscle. Thus no force is lost ; and the 

 bird is enabled to repeat the downward stroke much faster than if the 

 prismatic form of muscle had been retained. 



I have selected, in illustration of triangular muscles, the triangular 

 muscles of the fore and hind limbs of the tiger. I have selected 

 the tiger, because he is the strongest and the handsomest animal 

 with which we are acquainted ; and strength and beauty, as long as the 



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