BIRDS, 311 



legs. The number of toes (is) varies from five to two ; generally, 

 however, there are three directed forwards, and one backwards. 

 In many species there is a peculiar mechanism, by means of which, 

 when perched upon a branch, the weight of their body tends to 

 bend their toes, and, consequently, to make them closely embrace 

 it in their grasp an arrangement that permits them to repose in 

 a standing position without any danger of falling while asleep. 

 Perhaps the engraving (Fig. 338) will serve to illustrate this very 

 elegant contrivance. The muscle that bends the toes (a, b) arises, 

 not from the leg, but from the haunch (a) : becoming suddenly 

 converted into a thin tendon, it passes at b in front of the knee- 

 joint, enclosed in a sort of pulley ; it then winds round the bone 

 of the leg, to the back of the ankle-joint (b, c} y where it likewise 

 passes through a pulley at c hence it proceeds forwards behind 

 the tarsal bone to a 7 , where it divides into the sinews that bend 

 the toes. From this arrangement it will be seen that the weight 

 of the bird, by bending the knee-joint (b) and the ankle-joint (c), 

 puts the muscle (a, b, c, d) upon the stretch, and thus the toes are 

 made to grasp the branch without any effort. 



The feathers with which birds are clothed are structures of ad- 

 mirable contrivance : each feather is composed of a horny stem, 

 hollow at the base, and provided with a plume, or beard, consist- 

 ing of barbs, which in turn are furnished with barbules. The form 

 of the feathers varies much : some are destitute of any plume, and 

 resemble the quills of the porcupine ; others have stiff barbs, with 

 barbules that hook into each other, and thus form an expanse of 

 great strength and lightness ; others, again, have both the barbs 

 and barbules long, flexible, and unconnected, rendering them ex- 

 ceedingly soft and light ; and there are some composed of simple 

 down. Their colours are infinitely varied, and are often com- 

 parable to those of flowers, or the most brilliant gems, in beauty 

 and splendour. Generally, the plumage of the female is not so 

 richly ornamented as that of the male, and it is rare for the young 

 bird to be clothed in the same colours as the adult. Many like- 

 wise assume a plumage in the spring altogether different from 

 that of winter. The large stiff feathers that grow on the wings 

 of birds are called the wing-feathers or the pinion-feathers : they 

 extend the surface of the wings very considerably without add- 

 ing much to their weight, and convert them into powerful oars, 

 adapted to strike against the air with such force and frequency, 

 that the shock thus produced impels the animal in a direction 

 contrary to the stroke. The ability of a bird to sustain itself in 



