. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 4 1 2 Biology of the Vertebrates. maintains a rate of one hundred miles an hour, has about the best develop- ment of air sacs to be found in any bird. The pneumatic diverticula of the lungs of Chameleon, already men- tioned (Fig. 341), and those of certain other lizards may perhaps be regarded as prophetic of the air sacs of birds. (e) Mammals.—The lungs of mammals are usually characterized in two ways: first, by being subdivided externally into two lobes;
. Biology of the vertebrates : a comparative study of man and his animal allies. Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative. 4 1 2 Biology of the Vertebrates. maintains a rate of one hundred miles an hour, has about the best develop- ment of air sacs to be found in any bird. The pneumatic diverticula of the lungs of Chameleon, already men- tioned (Fig. 341), and those of certain other lizards may perhaps be regarded as prophetic of the air sacs of birds. (e) Mammals.—The lungs of mammals are usually characterized in two ways: first, by being subdivided externally into two lobes; and secondly, by showing some degree of asym- Anterior Lobe . , metry in accommodation to sur- rounding organs. When asymmet- rical the lobes are more numerous on the right than on the left side. Thus, in man (Fig. 345), there are three lobes in the right lung and two in the left. The upper- most odd lobe of the right lung lies behind the right pulmonary artery, while the absence of a cor- responding lobe on the left side permits the presence of the large left aortic arch. Certain mammals, as for example Cetacea, Sirenia, Proboscidea, Hyra- coidea, and most Perissodactyla, resemble other vertebrates in the absence of pulmonary lobes, while Monotremata are transitional, since they possess lobes only in the right lung. The lungs of whales, which are located rather posteriorly in the hulls of these seagoing leviathans, are probably hydrostatic as well as respiratory in function. Whales have a unique breathing apparatus that enables them, during a plunge into the ocean depths, to imprison air in the capacious nasal chamber which is several times larger than the brain case. In fact the nasal chamber occupies the major part of a whale's head and is capable of storing a generous supply of air that would otherwise be forced out of the lungs by the enormous pressure of the water. The apertures leading from the nasal passages to the lungs can be shut off by two plugs of tissue which f
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