. Elements of comparative zoology. Zoology. BIRDS. 351 terminated by claws; short in the terrestrial; longer in the arboreal, forms. Claws occur in some cases, espe- cially in young birds, upon the wings. In all living birds teeth are ab- sent, and even in the embryos but the slightest trace of their former existence can be found. In certain fossil birds well-developed teeth oc- cur (fig. 150). The tongue is usu- ally slender, stiff, and horny, and in some forms (woodpeckers, etc.) it is very extensible. The oesophagus is long, and frequently a part of it in the neck is swollen out to form a r
. Elements of comparative zoology. Zoology. BIRDS. 351 terminated by claws; short in the terrestrial; longer in the arboreal, forms. Claws occur in some cases, espe- cially in young birds, upon the wings. In all living birds teeth are ab- sent, and even in the embryos but the slightest trace of their former existence can be found. In certain fossil birds well-developed teeth oc- cur (fig. 150). The tongue is usu- ally slender, stiff, and horny, and in some forms (woodpeckers, etc.) it is very extensible. The oesophagus is long, and frequently a part of it in the neck is swollen out to form a reservoir of food, or crop. The stomach is divided into two parts. The first of these (proventriculus), which is glandular, appears much like an enlargement of the gullet. The second or muscular stomach (gizzard) is a veritable chewing organ. It is most developed in the grain or seed-eating birds, and in these often contains small stones to assist in grinding the food. The lungs are especially well de- veloped, and a peculiarity is that connected with them are air-sacs which extend among the other viscera and even into some of the bones, as those of the wing.* These air-sacs serve * A similar pneumaticity occurred in the bones of some of the fossil reptiles (Dinosaurs, p. 349).. Fig. 147.—A limentary tract of an eagle, c, crop; m, muscular stom- ach (gizzard); i, intes- tine; p, glandular stom- ach (proventriculus); t, trachea; v, 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 Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1904
