BIRD. 



3D 7 



little more meaning, to our larger divisions of the 

 several classes of animals, we would both shorten 

 and smooth the road to that accurate knowledge of 

 the individuals, which is the valuable, and indeed the 

 only valuable, part of the whole. Tlie other method, 

 that which takes but one portion of an organ us the 

 ground of resemblance, is simple only in proportion ; 

 as it teaches little, and simplest of all when it teaches 

 nothing. See the section on SYSTEMATIC AURANGK- 

 MENT iu this article ; and also the general article 

 CLASSIFICATION in its place in the alphabet. 



In all birds, the bending of the tibial and ttirsal | 

 joints has the same effect in the contracting or' the 

 muscles which close the toes. This may be seeu in ! 

 those birds which draw up one of their feet, either to 

 warm it, or to rest on the other; for the toes of the 

 foot which is drawn up are always clutched together, 

 and to open them out with the foot in that position 

 requires an effort. It even requires an effort in the 

 bird to keep the toes expanded. When it rests its 

 weight on the feet the weight causes the effort ; but 

 the toes of a dead bird are always partially closed, 

 which shows that a muscular exertion is necessary for 

 keeping them open when that is not effected by the 

 weight. When the bird is dead, the muscles, which 

 act both ways, are of course equally rigid, and the 

 toes close, to the degree at which the living muscles 

 would balance each other, and the leg be in a state 

 of repose. 



This tendency of the foot to close when the leg is 

 bent is effected in a very simple manner: the ten- 

 dons of the contracting muscles pass over the outsides 

 of the bent joints, and those of the extending ones 

 over the insides ; so that, by the bending, the former 

 are pulled much in the same way as if their muscles 

 were contracted and the latter are slackened in the 

 same way as if their muscles were relaxed. 



All feet which bear on the ground with jointed 

 toes, and partially even those which have hoofs, pos- 

 sess this property, though few of them possess it in 

 the same perfection as the feet of birds. 



And when we consider the difference of habit 

 between clutching, climbing, and perching birds, and 

 quadrupeds which have actions somewhat similar, we 

 can at om-e see that this property is most necessary 

 in the feet of the birds. Mammalia which clutch 

 prey with their paws have a point of rest for their 

 other feet, either on the body of the prey, or on some 

 other solid substance; and even in those climbing 

 mammalia which are the most dexterous leapers, the 

 spring is taken from the hind feet, and the gran, I use 

 of the fore ones is to catch hold at the end of the 

 leap. In slower climbers the one set of extremities 

 are always fast while the others are extended ; and 

 in the few mammalia (such for instance as the sloths) 

 which may be said to perch, the proper perching 

 apparatus is hooks so formed by the claws and toes 

 that the requisite shape is preserved by stops of bone. 

 Thus, as the flexible spine of the mammalia requires 

 to be borne up by two sets of supports, when it is in 

 a horizontal position, so when they are in action 

 they may be said to have always two points of sup- 

 port upon the ground or other surface which bears 

 them up, a fore and hind one, of the opposite sides, 

 alternately, when they walk ; and the two fore and 

 the two hind ones alternately when they bound and 

 leap. The former of these actions is confined almost 

 exclusively to the legs and feet, but in the latter the 

 spine comes more efficiently into play, as may be 



seen in the leaping of the cat tribe or in the coursing 

 of a greyhound. 



Birds deriving no support upon solid surfaces from 

 their anterior extremities, and having no action at 

 the spine to assist them in leaping, and yet having to 

 perch, and not only poise themselves, but find foot!, 

 construct nests, and perform other operations upon 

 perches far more unstable than any upon which the 

 mammalia have to rest, must be more sure-footed in 

 proportion. The slender sprays of trees, the flexible 

 stalks of herbaceous plants, "and all sorts of sub- 

 stances, not only of a yielding nature in themselves, 

 but exposed to the violent action of the winds, by 

 which both perch and percher are rocked at no mode- 

 rate rate, are all pathways to one race or other of the 

 feathered tribe. Nor, though at first sight such seems 

 to be the case, is that the footing most difficult to be 

 | maintained ; for, upon a bending twig or stem, the 

 | perch and percher soon acquire the same momentum, 

 I swing together, and have no more tendency to sopa- 

 | rate than water has to escape from a glass, when that 

 glu-s is set in one side of a hoop, and the hoop 

 whirled rapidly round on the opposite point. This 

 concert of motion, as we may call it, is general in 

 i mechanics, and the application of it is of great service 

 to all birds which feed or repose on perches of the 

 1 description alluded to. It is the resistance of the 

 bottom and sides of the glass to the centrifugal force 

 of the water, and the resistance of the hoop to the 

 same force in the glass, which keeps these three 

 together, or in concerted motion ; and in like manner 

 when a bird is rocked in the spray, all that it has to 

 do is to resist its own centrifugal force by the clutch 

 of the feet. 



But when the bird has to perch on the pinnacles 

 of the rocks, as is the case with the mountain eagles 

 and some of the other mountaineers, and also with 

 several of the more predatory and powerfully-winged 

 sea-birds, it has not the advantage of concerted motion 

 along with its perch, but must either abide at rest, 

 despise the tempest, or drift before its fury. The 

 habitations of those species which sit on the pinnacles 

 of rocks are the very homes of the tempests; for 

 winds war upon rifted shores and among rugged 

 mountains when the expanse of the sea and the plain 

 are still. Not only this, but these birds live much 

 upon the havoc which the tempests produce among 

 other creatures ; and thus it becomes necessary that 

 they should be enabled to remain on their watch- 

 towers, and mark its progress. But here, as in all 

 other cases, the purpose of nature is accomplished, 

 and accomplished by apparatus the most effective, 

 and at the same time the most simple. 



It is chiefly by the pulling of the tendons which 

 close the toes, by the mere action of bending the 

 joints of the leg, that this firmness on the perch is 

 maintained. Their tendons pull all the phalanges 

 of the toes ; and thus the same action, and that not a 

 muscular exertion, which would tire, but a state of 

 greater repose than when the legs are not bent, 

 enables the bird to hold on with the whole foot, and 

 the hold taken by the elastic pads and tubercles is 

 far more firm upon a hard substance than if it were 

 taken by means of claws. The rock perchers also, 

 in general, use their cla\\s in clutching and killing 

 their prey, so that they could not be used in keeping 

 the perch without blunting their points, and thus 

 unfitting them for their proper purposes ; neither 

 could a hold merely by means of the claws be kept 



