EXERCISE THE SEVENTH.
Of the abdomen of the common fowl and of other birds.
From the external orifice proceeding through the vulva we come to the uterus of the fowl, in which the egg is perfected, surrounded with the white and covered with its shell. But before speaking of the situation and connections of this part it seems necessary to premise a few words on the particular anatomy of the abdomen of birds. For I have observed that the stomach, intestines, and other viscera of the feathered kinds were otherwise placed in the abdomen, and differently constituted, than they are in quadrupeds.
Almost all birds are provided with a double stomach; one of which is the crop, the other the stomach, properly so called. In the former the food is stored and undergoes preparation, in the latter it is dissolved and converted into chyme.[143] The familiar names of the two stomachs of birds are the crop or craw, and the gizzard. In the crop the entire grain, &c. that is swallowed is moistened, macerated, and softened, and then it is sent on to the stomach that it may there be crushed and comminuted. For this end almost all the feathered tribes swallow sand, pebbles, and other hard substances, which they preserve in their stomachs, nothing of the sort being found in the crop. Now the stomach in birds consists of two extremely thick and powerful muscles (in the smaller birds they appear both fleshy and tendinous), so placed that, like a pair of millstones connected by means of hinges, they may grind and bruise the food; the place of teeth, which birds want, being supplied by the stones which they swallow. In this way is the food reduced and turned into chyme[143]; and then by compression (just as we are wont, after having bruised an herb or a fruit, to squeeze out the juice or pulp) the softer or more liquid part is forced out, comes to the top, and is transferred to the commencement of the intestinal canal; which in birds takes its rise from the upper part of the stomach near the entrance of the œsophagus. That this is the case in many genera of birds is obvious; for the stones and other hard and rough substances which they have swallowed, if long retained, become so smooth and polished that they are unfit to comminute the food, when they are discharged. Hence birds, when they select stones, try them with their tongue, and, unless they find them rough, reject them. In the stomach of both the ostrich and cassowary I found pieces of iron and silver, and stones much worn down and almost reduced to nothing; and this is the reason why the vulgar believe that these creatures digest iron and are nourished by it.
If you apply the body of a hawk or an eagle, or other bird of prey, whilst fasting, to your ear, you will hear a distinct noise, occasioned by the rubbing, one against another, of the stones contained in the stomach. For hawks do not swallow pebbles with a view to cool their stomachs, as falconers commonly but erroneously believe, but that the stones may serve for the comminution of their food; precisely as other birds, which have muscular stomachs, swallow pebbles, sand, or something else of the same nature, to crush and grind the seeds upon which they live.
The stomach of birds, then, is situated within the cavity of the abdomen, below the heart, lungs and liver: the crop, however, is without the body in some sort, being situated at the lower part of the neck, over the os jugale or merry-thought. In this bag, as I have said, the food is only macerated and softened; and several birds regurgitate and give it to their young, in some measure as quadrupeds feed their progeny with milk from their breasts; this occurs in the whole family of the pigeons, and also among rooks. Bees, too, when they have returned to their hives, disgorge the honey which they have collected from the flowers and concocted in their stomachs, and store it in their waxen cells; and so also do hornets and wasps feed their young. The bitch has likewise been seen to vomit the food which she had eaten some time before, in a half-digested state, and give it to her whelps: it is not, therefore, to be greatly wondered at, if we see the poor women, who beg from door to door, when their milk fails, feeding their infants with food which they have chewed and reduced to a pulp in their own mouths.
The intestines commence in birds, as has been said, from the upper part of the stomach, and are folded up and down in the line of the longitudinal direction of the body, not transversely as in man. Immediately below the heart, about the waist, and where the diaphragm is situated in quadrupeds, for birds have no [muscular] diaphragm, we find the liver, of ample size, divided into two lobes situated one on either side (for birds have no spleen,) and filling the hypochondria. The stomach lies below the liver, and downwards from the stomach comes the mass of intestines, with numerous delicate membranes, full of air, interposed; the trachea opening in birds, as already stated, by several gaping orifices into membranous abdominal cells. The kidneys, which are of large size in birds, are of an oblong shape, look as if they were made up of fleshy vesicles, without cavities, and lie along the spine on either side, with the descending aorta and vena cava abdominalis adjacent; they further extend into and seem to lie buried within ample cavities of the ossa ilia. The ureters proceed from the anterior aspects of the kidneys, and run longitudinally towards the cloaca and podex, in which they terminate, and into which they pour the liquid excretion of the kidneys. This, however, is not in any great quantity in birds, because they drink little, and some of them, the eagle for example, not at all. Nor is the urine discharged separately and by itself, as in other animals; but, as we have said, it distils from the ureters into the common cloaca, which is also the recipient of the fæces, and the discharge of which it facilitates. The urine is also different in birds from what it is in other animals; for, as the urine in the generality of animals consists of two portions, one more serous and liquid, another thicker, which, in healthy subjects constitutes the hypostasis or sediment, and subsides when the urine becomes cold; so is it in birds, but the sedimentary portion is the more abundant, and is distinguished from the liquid by its white or silvery colour; nor is this sediment met with only in the cloaca, (where it abounds, indeed, and surrounds the fæces,) but in the whole course of the ureters, which are distinguished from the coverings of the kidneys by their white colour. Nor is it only in birds that this abundant thicker renal secretion is seen; it is conspicuous in serpents and other ovipara, particularly in those whose eggs are covered with a harder or firmer membrane. And here, too, is the thicker in larger proportion than the thinner and more serous portion; its consistency being midway between thick urine and stercoraceous excrement: so that, in its passage through the ureters, it resembles coagulated or inspissated milk; once discharged it soon concretes into a friable mass.