. The chordates. Chordata. t LONGITUDINAL ®7W|| { MUSCLES ADVENTITIA VAGUS NERVE. Fig. 20. The esophagus as seen in cross section. (Right) A section of the entire esophagus. (Left) A small portion much enlarged. The ldyers of tissue characteristic of the entire alimentary canal are found in the esophagus. (After Braus. Courtesy, Neal and Band: "Chordate Anatomy," Philadelphia, The Blakiston Company.) rugae on the wall of the stomach (Fig. 21) and the transversely di- rected plicae which may occur in both the "small" and the "large" intestine (Fig. 23). The interna
. The chordates. Chordata. t LONGITUDINAL ®7W|| { MUSCLES ADVENTITIA VAGUS NERVE. Fig. 20. The esophagus as seen in cross section. (Right) A section of the entire esophagus. (Left) A small portion much enlarged. The ldyers of tissue characteristic of the entire alimentary canal are found in the esophagus. (After Braus. Courtesy, Neal and Band: "Chordate Anatomy," Philadelphia, The Blakiston Company.) rugae on the wall of the stomach (Fig. 21) and the transversely di- rected plicae which may occur in both the "small" and the "large" intestine (Fig. 23). The internal surface of the more anterior region of the intestine is usually thickly beset with delicate, long, cylindric pro- jections, the villi, which give the surface a velvety appearance and texture. Each villus consists of digestive epithelium enclosing a core of connective tissue filled with blood-capillaries and small lymph-vessels (Fig. 22). It is thus equipped for absorbing the digested food which bathes its surface. In cyclostome eels, sharklike fishes, and a few other fishes, an inwardly projecting fold of the intestinal lining extends lengthwise of the tube and winds spirally about it, in some cases mak- ing several or many spiral turns in its course from one end to the other (Fig. 23). This spiral valve greatly increases the functional surface of an otherwise short intestine. When the width of the spiral fold exceeds the radius of the intestine, as it commonly does, the fold necessarily becomes coiled upon itself in the axis of the intestine, thus occluding. 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 Rand, Herbert W. (Herbert Wilbur), 1872-1960. Philadelphia : Blakiston
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