Man only, and the swine, are subject to swellings in the throat, which are mostly caused by the noxious quality of the water[264] which they drink. The upper part of the gullet is called the fauces, the lower the stomach.[265] By this name is understood a fleshy concavity, situate behind the tracheal artery, and joining the vertebral column; it extends in length and breadth like a sort of chasm.[266] Those animals which have no gullet have no stomach either, nor yet any neck or throat, fishes, for example; and in all these the mouth communicates immediately with the belly. The sea-tortoise[267] has neither tongue nor teeth; it can break anything, however, with the sharp edge of its muzzle. After the tracheal artery there is the œsophagus, which is indented with hard asperities resembling bramble-thorns, for the purpose of levigating the food, the incisions[268] gradually becoming smaller as they approach the belly. The roughness at the very extremity of this organ strongly resembles that of a blacksmith’s file. CHAP. 69.—THE HEART; THE BLOOD; THE VITAL SPIRIT. In all other animals but man the heart is situate in the middle of the breast; in man alone it is placed just below the pap on the left-hand side, the smaller end terminating in a point, and bearing outward. It is among the fish only that this point is turned towards the mouth. It is asserted that the heart is the first among the viscera that is formed in the fœtus, then the brain, and last of all, the eyes: it is said, too, that the eyes are the first organs that die, and the heart the very last of all. The heart also is the principal seat of the heat of the body; it is constantly palpitating, and moves as though it were one animal enclosed within another. It is also enveloped in a membrane equally supple and strong, and is protected by the bulwarks formed by the ribs and the bone of the breast, as being the primary source and origin of life. It contains within itself the primary receptacles for the spirit and the blood, in its sinuous cavity, which in the larger animals is threefold,[269] and in all twofold at least: here it is that the mind[270] has its abode. From this source proceed two large veins, which branch into the fore-part and the back of the body, and which, spreading out in a series of branches, convey the vital blood by other smaller veins over all parts of the body. This is the only one[271] among the viscera that is not affected by maladies, nor is it subject to the ordinary penalties of human life; but when injured, it produces instant death. While all the other viscera are injured, vitality may still remain in the heart. CHAP. 70.—THOSE ANIMALS WHICH HAVE THE LARGEST HEART, AND THOSE WHICH HAVE THE SMALLEST. WHAT ANIMALS HAVE TWO HEARTS.