. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Fig. 254. A fish that has swallowed another fish larger than itself. fourteen inches, the lower end piercing the diaphragm to enter the body cavity before joining the stomach. It is only this short portion within the body cavity that is provided with a serosa layer of tissue outside the muscular and mucosa layers. A noteworthy differentiation of the esophagus in birds is a lateral enlarge- ment known, as the crop (Fig. 255), which may serve simply as a con
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. Fig. 254. A fish that has swallowed another fish larger than itself. fourteen inches, the lower end piercing the diaphragm to enter the body cavity before joining the stomach. It is only this short portion within the body cavity that is provided with a serosa layer of tissue outside the muscular and mucosa layers. A noteworthy differentiation of the esophagus in birds is a lateral enlarge- ment known, as the crop (Fig. 255), which may serve simply as a convenience for the temporary storage of food hastily secuied in the presence of enemies or competitors, as in the case of seed-eaters generally, or may be supplied with glands which act chemically upon the food eaten. Pigeons produce a cheesy nutritious substance from the lining of the crop, called "pigeon's milk," that is fed to nestlings by regurgitation. The tropical hoactzin, Opisthocomus, has a muscular crop which works mechanically upon the food that finds lodgment in it. A chicken going to roost with its crop filled with corn, falls asleep unham- pered by the continuous effort of pick- ing up food and "feeds" all night long while resting, as the crop, like the hopper of a gristmill, releases its con- tents automatically and periodically to the glandular stomach and grinding gizzard as needed. Among the lower vertebrates any external line of demarcation between the esophagus and stomach is either absent or vague, but in birds and mammals there is usually a definite point of transition. In many cases it is easier to gain entrance to the stomach from the esophagus than to escape from the stomach into the intestine. £s? Pancreas. Proventriculus ~ -Liver '"•Gizzard =^7~Small Intestine Colic Caeca "Cloacal Opening Fig. 255. Digestive tract of a hen. 3. Stomach The stomach is a conspicuous enlargement of the digestive tract lying between the esoph
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Keywords: ., bookcentury1900, booksubjectanatomycomparative, booksubjectverte
