. Human physiology : designed for colleges and the higher classes in schools and for general reading . aces, made very hard, so that by rub-bing together they bruise the grains; and while they arethus ground, as between two millstones, the gastric juiceis poured down upon them from above. This arrangement isseen in Fig. 21, which represents the digestive apparatus in theturkey laid open. At b is the gizzard, showing the two hardsurfaces, which are rubbed together by the stout muscles thatmake the great bulk of the organ. Above, at a, are theglands which pour forth the gastric juice. And above
. Human physiology : designed for colleges and the higher classes in schools and for general reading . aces, made very hard, so that by rub-bing together they bruise the grains; and while they arethus ground, as between two millstones, the gastric juiceis poured down upon them from above. This arrangement isseen in Fig. 21, which represents the digestive apparatus in theturkey laid open. At b is the gizzard, showing the two hardsurfaces, which are rubbed together by the stout muscles thatmake the great bulk of the organ. Above, at a, are theglands which pour forth the gastric juice. And above thispart of the stomach there is, in all grain-eating birds, a largesac bulging out from the oesophagus, called the crop, which isa reservoir for the food, just as the paunch is in the ruminatinganimals. In those birds that live on flesh or fish there is nosuch grinding apparatus; and the walls of the stomach arequite thin, and it presents no hard surfaces. 96. It would be interesting, were it consistent with the plan DIGESTION. 63 Digestion in the turkey. Digestive apparatus in different STOMACH OF THE TURKEY. of this book, to go into a further examination of the varietiesin the digestive apparatus in different animals. They have avery wide range, being according to the wants of the animal ineach case. The kind of food, the mode of life, and the pur-pose which the animal is designed to fulfill, are the circumstanceswhich govern these variations. The proportion which the di-gestive apparatus bears-to^pther parts varies very much ; andin some of the lower orders of animals, the body seems to beall stomach. In such cases, the only appendages are those whichseize the food and direct it into the orifice of this organ. This 64 HUMAN PHYSIOLOGY. Apparatus of the circulation. Heart, arteries, veins, capillaries. is the case with the hydra, represented in Fig. 1. And, whatis very singular, the outside of the body of this animal is justas capable of acting as a stomach as its
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