Class-book of physiology : for the use of schools and families : comprising the structure and functions of the organs of man, illustrated by comparative reference to those of inferior animals . rtion as the cells become more numerous in a givenspace. Thus, in the entire group of warm-blooded ani-mals, where the function of respiration ie at its highestperfection, we find an almost infinite number of cells. 95. In the human lungs it is estimatedthat there are at least six hundred millionsof air cells, collectively presenting a surfaceequal in extent to about thirty times thewhole surface of the
Class-book of physiology : for the use of schools and families : comprising the structure and functions of the organs of man, illustrated by comparative reference to those of inferior animals . rtion as the cells become more numerous in a givenspace. Thus, in the entire group of warm-blooded ani-mals, where the function of respiration ie at its highestperfection, we find an almost infinite number of cells. 95. In the human lungs it is estimatedthat there are at least six hundred millionsof air cells, collectively presenting a surfaceequal in extent to about thirty times thewhole surface of the body. Each cell, as isrepresented in fig. 19,1s constructed on thebranchingZftt same Plan as tne sinSle air-sac of the snail,and consists of a thin delicate membrane, with an artery Describe the respiratory organs of a bird. How do birds compare withother animals in the frequency of their respirations? What special benefitdo bird3 derive from the large amount of air contained in their sacs and bones?Upon what does the capacity of the lung depend ? In what group of animalsare the air cells most numerous? How many air cells are there in theVuman lungs ? How is each air cell constructed ?. RESPIRATION. 53 distributed on its surface in minute capillary vessels, whichterminate in veins that carry the blood back to the heart. 96. The whole substance of the lungs is thus made upof these minute cells, with their air and blood vessels. 97. The lungs are suppliedwith air through the larynx andtrachea. {Fig. 20.) 98. The larynx is an irregularcartilaginous tube, forming theupper extremity of the windpipe,as the whole tube is commonlycalled. The larynx is situatedimmediately below the root ofthe tongue, and forms the pro-tuberance in the front part of theneck, called Adams larynx gives passage to theair which is inhaled into thelungs or exhaled from them, and Contributes essentially tO the pro- Fig. 20.—a, the larynx; b, the trachea;. J , * c, bronchial tubes; d, the left lung
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