. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Intake Apparatw 3°5 tube between the pharynx and the stomach (Fig. 253), is primarily a sphincter, the office of which is to forward food by peristalsis along its course to a point beyond normal control. The peristaltic action of the walls of the esophagus is well shown by a horse drink- ing at a brook, for the gulps of water taken in have to travel up hill along the neck and their passage is externally vis- ible. In the case of a snake the violent perista
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Intake Apparatw 3°5 tube between the pharynx and the stomach (Fig. 253), is primarily a sphincter, the office of which is to forward food by peristalsis along its course to a point beyond normal control. The peristaltic action of the walls of the esophagus is well shown by a horse drink- ing at a brook, for the gulps of water taken in have to travel up hill along the neck and their passage is externally vis- ible. In the case of a snake the violent peristalsis necessary in swallowing a com- paratively large morsel of food, such as a frog, is supplemented by the muscles of the body wall. When not in use the esophagus col- lapses to modest dimensions, but upon occasion it is capable of great temporary distension. There are certain fishes that can even swallow another fish larger than themselves (Fig. 254). In many verte- brates the inner lining of the esophagus is characterized by expansive longitudi- nal folds that allow for a sudden increase in diameter during the act of swallow- ing, but at other times contract so that the tube may occupy a minimum of space. The inner lining of the esophagus of marine turtles is beset with backward- projecting horny papillae, which enable them more easily to swallow the slippery seaweeds upon which they habitually feed. The length of the esophagus is de- pendent largely upon the presence or ab- sence of a neck. In frogs and toads the neck is reduced to a minimum so that a fly entering the mouth of one of these animals finds itself almost immediately landed in the stomach, whereas in long-necked animals, such as the giraffe for example, the esophageal adventures of food are much more extended. In adult man the length of the esophagus is approximately. Fig. 253. General diagrammatic view of the digestive system in man. The liver has been tipped anteriorly to show the gall bladder and common bile
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
