B I R D. 



401 



nicety of observation which they would require, over- 

 come. In the first place, we know not, and we cannot 

 ascertain, the relative surfaces of the blood-vessels 

 exposed to the air in lungs only, and in the whole 

 system, as in birds ; and, in the second place, we 

 know not the difference of action which the air may 

 have on the coat of a very small blood-vessel, such 

 as those in the lungs, and that of a larger one. We 

 do know that the exposed surface of the vessels in 

 the lungs must form but a small portion of that of 

 the whole vessels in the system, because in the freest 

 breathers, that is, what is usually styled the " longest 

 winded" of the mammalia, which have their blood 

 aerated in the lungs only, or chiefly, the portion 

 which passes through these organs at each respira- 

 tion of the breath, is only a small fraction of the 

 whole. We know also that the coats of the larger 

 blood-vessels must, in order that the vascular system 

 may have equal strength in all its parts, have their 

 coats much thicker and firmer than the smaller ones, 

 though we cannot precisely say in what proportion ; 

 neither do we know to what extent the difference of 

 thickness in the coats of the vessels diminishes the 

 action of the air upon the contained fluid. Perhaps 

 the thickness of the coats is directly, arid the action 

 of the air inversely, in some such ratio as that of the 

 squares of the diameters of the different vessels ; but 

 this is a mere theoretic guess, undemonstrated, and 

 incapable of demonstration. 



Analogy shows, however, that the advantages which 

 birds derive from this general admission of air to the 

 blood-vessels is very great. The race-horse is quite 

 fatigued with a few miles at his full speed, and so is 

 the greyhound, while the lion himself is in need of 

 repose after a single leap. But birds can maintain 

 their rapid flight during the livelong day, and for 

 hundreds of miles upon the stretch ; and when they 

 d, as is sometimes the case, drop down in agitation 

 or in exhaustion, the former seems generally to be the 

 effect of fear, and the latter of muscular fatigue, for 

 they do not pant as the mammalia do when they 

 have over-exerted themselves. 



But the advantage in the aeration of the blood is 

 not the only one which birds derive from this pecu- 

 liarity of their structure. The same air which exerts its 

 renovating influence upon the blood, supports all the 

 more delicate structures which it readies and sur- 

 rounds, as a cushion of the most perfect softness and 

 elasticity ; so that, by the most rapid motion, and the 

 most violent twitches which the body receives in the 

 changes and turnings of that motion, there can be no 

 concussion of the parts more immediately necessary 

 for the life of the bird. 



We should now proceed to consider the productive 

 system in buds, the progress of the egg, the processes 

 of nidification and incubation, and the attention of 

 the parent birds to their young ; but the egg itself 

 can be more advantageously noticed in comparison 

 with the eggs of other animals ; and the principles 

 of nest-making require a knowledge of the haunts 

 and habits of birds, as well as of their vital functions. 

 The one part of the subject can, therefore, be better 

 explained in the article OVIPAIU, and the other in 

 the article NEST. We shall, therefore, here close this 

 section, the various topics involved in which no ex- 

 planation could exhaust ; and of which we take leave 

 with feelings of regret, as one of the most interesting 

 and fascinating with which the student of nature can 

 be occupied. 



iN.-v i . HIST. Vol.. I. 



II. EXTERNAL PARTS OF A BIRD. The subjects 

 to be noticed in this section are much less interesting 

 and instructive than those slightly glanced ;-.t in the 

 former one ; but as the descriptions of all Lirds are 

 founded chiefly upon the colours of the external parts, 

 and as these are all that we know about thoi-e species 

 which belong to science only as museum specimens, 

 this part of the subject becomes necessary in a gene ml 

 article descriptive of (he class. Its minor importance 

 will, however, enable us to treat it more hrieflv. 



The external parts of birds, as they immediately 

 present themselves to the eye, consist of throe kind's 

 of surfaces horn, naked skin, and feathers. The 

 first of these requires little description, being only the 

 bill, the claws, and partially the scaly coverings of 

 the naked parts of the feet and toes, and is most con- 

 spicuous on the upper sides of the toes, and the ante- 

 rior sides of the tarsi. The naked surfaces are also 

 limited in extent, being confined to the head, portions 

 of the neck in some genera, and those nni'cathered 

 parts of the feet and toes which are not covered by 

 horny scales. The feathered parts are much more 

 important in the popular description of birds, as it is 

 to their forms and colours that the attention is first 

 attracted. 



The horny surface of birds varies in hardness in 

 different species, and may, in general, be said to be 

 firm in its texture in proportion as it is dark in colour. 

 The more powerful birds of prey have the beak and 

 claws black, with a slight bluish tinge ; but some 

 even of these have them yellow when in the imma- 

 ture state, whatever may be the colour when they are 

 full grown. This change of colour in horny * sub- 

 stances appears to be the effect of atmospheric air and 

 light ; and it is not confined to birds, but takes place 

 in the hoofed mammalia, the young of which, in gene- 

 ral, have the hoofs yellow, though they turn black 

 after a short time. The forms of the bills and the 

 claws of birds, being closely connected with some of 

 their principal habits, will be noticed in another sec- 

 tion of this article. 



The naked skin of birds has generally a porous or 

 spongy appearance ; and in many speeies it has a 

 bloom of colour in the living state, which is often very 

 brilliant, and displays an iridescence which is not 

 very easily describable, but. which fades the instant 

 that life is extinct. The bills of some birds, such for 

 instance as the toucans, is covere i with a membrane, 

 in which there is a similar display of colour, that 

 fades in the same manner ; but in most birds these 

 portions df naked membrane with perishable colours 

 are on other parts of the body. When there is a 

 naked membrane reflected on the upper mandible of 

 the bill at its base, that membrane is called a /<', from 

 its surface having some resemblance to that of wax. 

 When it extends to, or surrounds the eye, it. is called 

 a lore, which means an armature, or covering. Some- 

 times there is only a naked spot or tubercle over the 

 eye ; in other cases there is a projection of naked skin 

 on the top of the head, as in the domestic cock, which 

 is called a cumb, because it is often pectinated, or 

 divided in its margin. Sometimes also there are 

 pendent portions of naked skin hi'.nging from the 

 sides of the under-jaw, or from the cheeks, and those 

 are called wattles. In some instances the anterior 

 portion of the throat is entirely covered by tuhcrcu- 

 lated portions of naked skin; and that is often 

 capable of inflation, as in the case of a male turkey. 

 In other instances, again, the entire neck and greater 

 K K 



