The Anatomy of a Bird
It is very important that every one who studies birds should have some acquaintance with their insides as well as with their outsides. To have a proper appreciation of the mechanism of flight, the most distinctive attribute of a bird, we must explore the air reservoirs and muscles, which combine, with other organs, to form a complicated, but exquisitely adjusted, system. It is true that other animals show a similar adaptation to their several modes of life, but in a bird the necessities of life seem to have produced a more obvious and striking harmony between structure and habit. Furthermore, the young ornithologist should not be content with gaining the ability to recognise the different kinds of birds: he should understand their mutual relations, and the place of a bird in Nature. To form an opinion about these matters needs more than an acquaintance with the colours and outward form, and with the eggs and nest. A great deal can be learnt from these characters, but they are at most only useful in linking together closely related species. All the members of the extensive tribe of parrots, for example, are bound together by their hooked bills, their white eggs, their grasping feet, &c. But we want to go further, and determine what are the relations of the parrots to other birds which differ totally from them in all outward and visible signs. To solve, or rather to attempt to solve, broader questions of this kind we must have recourse to the scalpel, and even to the microscope. Besides, there not only are birds, but there were birds, which have now passed away utterly, leaving behind only a few bones embedded in the rocks. Nothing of an external nature will avail us in considering what these birds were like in their day, and which of existing kinds they most resembled. We must have a knowledge of bones, of osteology, to grapple with the problems which they present. For these reasons I have dealt in the following pages principally with the organs of flight, and with those internal and external characters which are admitted to be of most use in classificatory questions. I have paid less attention to those organs which are not of importance from these points of view.