human figure it is at once seen to be the knee, and on referring to the same letter in the leg of the bird, we shall find that it is the true knee also; for supposing it to kneel, that is, to bend its leg, so that the fore part of the joint should touch the ground, it can only do so at the joint в, it being as obviously impossible from the structure of the joint c, that it

could bend the part C D forwards, so as to make the front part of the joint c touch the ground, as it would be for us to bend the leg-bone forward below the knee. The remaining portion, then, c D, of the bird's limb, when compared with the similar part in our own leg, ought to be called its ankle, and so in truth it is. This may be more easily understood by referring to a very extraordinary-looking bird, sometimes, though very rarely, seen in England, called the Black-winged Stilt, from the strange disproportion of its legs, a figure of which is annexed, and of which No. 2 may be considered as an illustration; in which an inexperienced observer will at first sight not easily persuade himself that C D is nothing more than the ankle, and the back part of the joint c its heel; yet so it is, as the reader will at once perceive in the following figure, where the

bird is represented in its usual, and what may be called, kneeling position; the real knee, corresponding with B in fig. 2, of the leg being partly hid in the feathers, and the bend of the leg beneath the tail corresponding with c, the remaining part from that point to the claws answering to our foot and

There are some other beautiful contrivances in the limbs of birds, which deserve attention. Look at a bird fast asleep with its head under its wing, resting usually on one leg, and that again resting upon a perch not thicker than one's finger. How apparently difficult and uneasy is such a position! and yet it is all made easy and safe to the bird by an admirable piece of internal mechanism, which may be briefly thus explained. Connected with the thigh-bone and leg, a set of muscles run down to the very extremity of the toes, so contrived and placed, that when, by pressure downwards, the limb bends, these fine muscles are pulled in, and therefore contract the toes, thus making them grasp more firmly whatever the bird is resting upon; just as if a set of fine strings ran over pulleys to certain hooks, and were acted upon at the other end by a weight or pressure, and thereby made to draw in the hooks.

But there are some birds, and very large ones too, such as

Herons, Cranes, and certain other wading birds, which sleep standing on one foot, the leg being kept perfectly straight; and in these birds, as the foot rests upon the ground, any grasping power acting upon the toes would be useless. In this case, therefore, what is required is some contrivance to keep the leg firm, that it may not give way, in consequence of any swinging or balancing motion of the body, which would inevitably overset the sleeper. Accordingly, the upper part of what we shall call the heel-bone, at c, is fitted in a very curious manner into the lower part of the leg-bone above it, and precisely answers the purpose required of the bird, affording a sufficient degree of resistance by the bending of the leg, to counteract the effect of any overbalancing of the body. The bird, moreover, has a power over this well-contrived prop, and thus bends its leg or keeps it perfectly stiff, as best suits its convenience.

CHAPTER III.

Internal Structure.-Digestive Organs.-Gullet, Crop, Stomach.— Adaptation of, to different Habits of Birds.-Gastric Juice, its Use and Properties. -Gizzard, its Grinding Powers.-Respiration of Birds.

HAVING briefly pointed out the most prominent features of the skeleton, as influencing the general form of birds, we shall now proceed to give a short sketch of the structure and uses of some of the internal parts, commencing with those for the supply and consumption of food. The following figure may assist our explanation.

The gullet (œsophagus), A, opens into the crop (ingluvies) B, which forms a sort of bag; on quitting this it extends to what is called the second stomach, c (infundibulum, or ventriculus succinturiatus), usually funnel-shaped, from whence it opens into the third stomach or gizzard, D (ventriculus callosus), communicating with the intestinal canal or bowels, E, which vary very much in length in different birds, though on the whole they are shorter than in the class of four-footed animals. The annexed plate is merely intended to convey a general idea of the stomachs of birds, and must by no means be depended upon as an accurate representation applicable to any particular family, since in each there is a marked variation with respect to the size, form, and other internal arrangements; a full explanation of which, though extremely interesting, from the beautiful adaptation to the habits of the bird, cannot in this little work be attempted; a few, however, may be briefly pointed out.

Thus, in what are called the carnivorous birds, feeding on

flesh, or fish, containing hair, feathers, or bony substances, which are of difficult digestion, the gullet is of a vast size and capacity compared with the other parts, often exceeding in width the stomach itself. In some of the water-birds it is large enough to contain even a whole fish till the proper stomach is ready to receive it. In watching Cormorants at a distance with a telescope, they may be sometimes seen quietly

reposing, with their mouths half open, and the tail of a fish hanging out, the remainder gorged in their capacious gullet: and Sea-Gulls will swallow bones of three or four inches in length; the lower end only reaching the stomach, whilst the rest continues in the gullet, and slips down gradually, in proportion as these lower ends are consumed.

The usual food of Gulls consists of fish; but when confined they will thrive very well on a diet with which they must be perfectly unacquainted by the sea side. We may form, too, some idea of their voracity, from the quantity consumed by a Gull kept and fed in a garden, which devoured in one day fourteen mice and two rats. Another was seen to swallow an