. Elementary biology; an introduction to the science of life. Biology. 84 ELEMENTARY BIOLOGY having the consistency of a rather thick pea soup, and all of it has passed on into the intestine. 119. The intestines. There are two distinct parts, or divi- sions, of the gut among the highest animals. The first part is called the small intestine, and in human beings it is about one inch in diameter and about twenty-four or twenty-five feet long. The small intestine opens rather abruptly into the large intestine, which is about two inches in diameter and about five feet long (see Fig. 28, y, k). The
. Elementary biology; an introduction to the science of life. Biology. 84 ELEMENTARY BIOLOGY having the consistency of a rather thick pea soup, and all of it has passed on into the intestine. 119. The intestines. There are two distinct parts, or divi- sions, of the gut among the highest animals. The first part is called the small intestine, and in human beings it is about one inch in diameter and about twenty-four or twenty-five feet long. The small intestine opens rather abruptly into the large intestine, which is about two inches in diameter and about five feet long (see Fig. 28, y, k). The wall of the intes- tine is rather thin and soft. You have probably handled a piece of pig gut or calf gut, which is used as sausage casing. In the living animal the wall of the intestine is not so hard and stiff as we sometimes find it in the sausage casing. This wall is made up of several layers of tissue. The inner lining carries very small glands, and the outer layers contain muscle cells. To this extent the wall of the intestine is like the wall of the stomach. The muscle cells of the gut are arranged in rings, so that when they contract they simply reduce the diameter of the intestine at any given point. The contraction starts at the forward end — that is, the end nearest the stomach — and passes backward along the whole length of the small intestine, aided by longitudinal muscles. As a result of this wave of contraction some of the thick mixture of food and digestive juices is moved along, a short distance. Fig. 30. Glands of the stomach The gastric juice is poured into the stomach through tubes, (7, which are hned by a layer of delicate cells ; it is produced by special gland cells, b, from materials brought by the blood in fine vessels, c. ( X 200). Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original
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