Human physiology (Volume 2) . ogether in his respiratorysystem, proceed either directly or indirectly. Of these, the mostimportant is the e. Respiration of concluding the subject of respiration, we may briefly advertto the different modes in which the process is effected in theclasses of animals, and especially in birds, the respiratory organsof which constitute one of the most singular structures of the ani-mal economy. The lungs themselves, — as in the marginal figureof the lungs, &c of the ostrich, (Fig. 152,)-are comparativelysmall, and are adherent to the chest,—wher
Human physiology (Volume 2) . ogether in his respiratorysystem, proceed either directly or indirectly. Of these, the mostimportant is the e. Respiration of concluding the subject of respiration, we may briefly advertto the different modes in which the process is effected in theclasses of animals, and especially in birds, the respiratory organsof which constitute one of the most singular structures of the ani-mal economy. The lungs themselves, — as in the marginal figureof the lungs, &c of the ostrich, (Fig. 152,)-are comparativelysmall, and are adherent to the chest,—where they seem to beplaced in the intervals of the ribs. They are covered bv thepleura only on their under surface, so that they are, in fact on theoutside oi the cavity of the chest. A great part of the thorax aswell as of the abdomen, is occupied by membranous air-cells intowhich the lungs open by considerable apertures. Besides these a Op. cit. p. 475. o Dr. Carpenter, Human Physiology, p. i3S) Lond lU2 OF ANIMALS. 65. cells, a considerable portion of the skeleton forms receptacles forair, in many birds ; and if webreak a long bone of a bird offlight, and blow into it, thebody of the bird being im-mersed in water, bubbles of airwill escape from the bill. Theobject, of course, of all this, isto render the body light, andthus to facilitate its the largest and mostnumerous bony cells are foundin such birds as have the high-est and most rapid flight, asthe eagle. The barrels of thequills are likewise hollow, andcan be filled with air, or emp-tied at pleasure. In additionto the uses just mentioned,these receptacles of air dimi-nish the necessity of breathingso frequently, in the rapid andlong-continued motions of se-veral birds, and in the greatvocal exertions of singingbirds. In fishes, in the place oflungs we find branchiae or gills,which are placed behind thehead on each side, and have a moveable gill-cover. By the throat, which is connected with theseorgans the
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