DIGESTIVE APPARATUS OF BIRDS. 381 very soft; in most granivorous Birds it is dry, triangular, and beset towards the base with small cartilaginous points; and in some insectivorous Birds, its extremity is armed with hooks or is jagged. The salivary glands are placed under the tongue, and consist of a mass of small rounded follicles; the saliva is generally thick; and sometimes it is quite glutinous. 344. The Pharynx is not separated from the mouth by a movable partition, as in the Mammalia; and has no peculiarities. The Esophagus (Fig. 201) beginning at the inferior part of the neck, communicates with the first digestive cavity named the crop; the sides of which are membranous. The food remains for a certain time in this first stomach, whose form and size vary. It is in the granivorous Birds, that the crop is most developed; it is also found in Birds of Prey; but it is wanting in the Ostrich, and in most Birds that feed on Fish. Below this part the Esophagus is again contracted, and presents further down a second dilatation, called the ventriculus succenturiatus, whose internal surface is perforated by a considerable number of small pores, communicating with follicles that secrete the gastric juice; in general, the size of the stomach is small; but in Birds deficient in the crop it is larger than usual, and seems to take the place of it. The ventriculus succenturiatus opens below into a third stomach named the gizzard; in which the process of chymification is completed. This varies much in capacity; but it is particularly in the structure of its walls, that important differences appear. In Birds that feed on flesh only, the sides of the gizzard are thin and membranous; but in those that swallow food, which is harder and more difficult to digest, it is furnished with strong muscles, intended to compress and to grind down its contents. This organ is most muscular in granivorous Birds; the thickness of its fleshy sides is considerable; and its inner surface is covered with a sort of almost cartilaginous epithelium. Its strength is immense; in the Ostrich for instance, the hardest bodies have been ground down by its contractions; and it evidently takes the place of an apparatus for mastication. 345. The Intestine, which forms the continuation of this DIGESTIVE APPARATUS OF BIRDS. 383 series of stomachs, is much shorter than in most Mammalia; but is composed, as in them, of two portions;-the small and the large intestine. The former, after having taken its first bend, turns in different directions; the second differs from it but little, and is not much enlarged; but it is generally distinguished by the existence, at the point of their junction, of two tubular appendages, ending with a "cul-de-sac," which are termed cæca (ANIM. PHYSIOL., § 214). These appendages are wanting, or at least are very small, in most Birds of Prey; but they are generally long and large in granivorous and omnivorous Birds. 346. The Liver is very large, and fills a great part of the chest, as well as of the upper portion of the abdomen,-these two cavities not being separated, as the Diaphragm is scarcely developed. This gland is divided into two nearly equal lobes, and generally gives origin to two hepatic canals, which, after uniting, terminate in the intestine. There is almost always a gall-bladder, which receives only a portion of the bile, and sends it into the intestine by a separate canal.-The Pancreas (sweetbread) is lodged in the first bend of the small intestine; it is generally long, narrow, and more or less divided.-The Kidneys are large, and are lodged in hollows excavated in the upper part of the pelvis; there is no urinary bladder; but the ureters terminate, as do also the oviducts, in the dilated extremity of the rectum, which is termed the cloaca (Fig. 201). The urinary excretion is almost entirely composed of uric acid, which is not soluble; and the amount of water in it is very small. 347. The nutritious products of digestion are conveyed from the intestine into the general circulation, by the lacteals; which by their union form two thoracic ducts; these open into the jugular veins on each side of the base of the neck, as in Mammalia (ANIM. PHYSIOL., § 266).-The blood of Birds is richer in red particles than that of the Mammalia; and these bodies, instead of being circular, are elliptical in form. There is nothing peculiar in the manner in which this fluid circulates; and the course it takes is the same as in the Mammalia. The blood passes from the left ventricle of the heart, into the arteries which distribute it to the several organs of the body; it returns into the right auricle, and from thence is carried to the right ventricle, which sends it to the lungs through the pulmonary arteries; it returns again to the heart, enters the left auricle, and completes the circulation by passing into the left ventricle, from which it set The heart has the same form, the same structure, the same out. position, and the same coverings as in the Mammalia; the walls of the left ventricle are extremely thick, and the right ventricle surrounds it on the right, and below, without prolonging itself to the point of that organ. The Aorta at its origin divides into CIRCULATING AND RESPIRATORY APPARATUS. 385 three large branches; of which the two first subdivide into the trunks that convey the blood to the head (the carotid arteries), to the wings (the subclavian), and to the muscles of the chest (the mammary, which are of large size in Birds, on account of the great development of those muscles, whose office is to draw down the wings); whilst the third curves downwards around the right bronchus, and constitutes the descending aorta. There are some peculiarities in the mode of distribution of the arteries; but they are not important, and it is only to be remarked, that in different points of the body they constitute remarkable plexuses, by frequently anastomosing together. The venous system terminates in three large trunks; one of which is analogous to the Vena Cava of the Mammalia; and the two other nearly correspond with the two subclavian veins, which do not unite to form a common trunk (or superior vena cava), as in these last animals. 348. The apparatus of Respiration presents more remarkable peculiarities than that of circulation. The lungs, as we have already said, communicate with large cells hollowed in the cellular tissue, and thus transmit the air into all parts of the body (Fig. 203); so that the respiration may be regarded as double, |