. Beginners' Zoology . pties into the straightrectum, which terminates in awidened part called the only the intestine, but thetwo ureters of the urinary systemand the two genital ducts of thereproductive system all empty intothe cloaca (Figs. 304, 305). The lungs have their rear sur-faces attached to the spinalcolumn and ribs (/«, Fig. 304).They are connected with thin-walled, transparent air sacs whichaid in purifying the blood. Wheninflated with warm air, they prob-ably make the body of the birdmore buoyant. For the names,location, and shape of severalpairs of air sacs, see Fig. 3
. Beginners' Zoology . pties into the straightrectum, which terminates in awidened part called the only the intestine, but thetwo ureters of the urinary systemand the two genital ducts of thereproductive system all empty intothe cloaca (Figs. 304, 305). The lungs have their rear sur-faces attached to the spinalcolumn and ribs (/«, Fig. 304).They are connected with thin-walled, transparent air sacs whichaid in purifying the blood. Wheninflated with warm air, they prob-ably make the body of the birdmore buoyant. For the names,location, and shape of severalpairs of air sacs, see Fig. connection of the air sacs withhollows in the humerus bones is also shown in the of the dones are hollow; this adds to the buoyancy ofthe bird. The pulmonary artery, as in man, takes darkblood to the lungs to exchange its carbon dioxide foroxygen. Of two animals of the same weight, which ex-pends more energy, the one that flies, or the one that runsthe same distance ? Does a bird require more oxygen. Fig. 306.—Position of LungsAND Air Sacs (Pigeon). Tr, windpipe; P, lungs; Lm, sacunder clavicle with prolongation(Ui) into humerus; La, sacs inabdomen. BIRDS i6s
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Keywords: ., bookcentury1900, bookdecade1920, bookidbeginnerszoo, bookyear1922
