. A text-book in general physiology and anatomy. Physiology, Comparative; Anatomy. 318 KESPIEATION which are provided with cilia. (See Fig. 135.) These cilia, together with the mucus secreted by the cells, serve to catch any particles of dust that may have passed the nasal cavity. The cilia are in constant motion, bending quicldy upward and then slowly returning to place, and in this manner forcing the collected particles steadily upward toward the pharjmx. The cartilage rings do not completely inclose the tube, but are shaped like the letter C, the open part being at the back and leaving a po
. A text-book in general physiology and anatomy. Physiology, Comparative; Anatomy. 318 KESPIEATION which are provided with cilia. (See Fig. 135.) These cilia, together with the mucus secreted by the cells, serve to catch any particles of dust that may have passed the nasal cavity. The cilia are in constant motion, bending quicldy upward and then slowly returning to place, and in this manner forcing the collected particles steadily upward toward the pharjmx. The cartilage rings do not completely inclose the tube, but are shaped like the letter C, the open part being at the back and leaving a portion of the tube soft and com- pressible. The gullet lies against this soft groove, and thus room for expansion is given as the food passes down the gullet. Structure of the lungs.— These are merely membranous sacs with an internal framework composed of the branch- ing bronchial tubes and air sacs. These treelike tubes are bound together with a soft, pink connective tissue, rich in elastic fibers, and over the whole is stretched an elastic mem- brane known as the plem-a. The bronchi and bronchial tubes are continuations of the trachea, and the larger ones resemble it in struc- ture with the exception that the cartilage rings are not so regularly arranged. As the tubes become smaller their walls become thinner, and finally the cartilage rings dis- appear entirely in the smaller tubes, while the mucous membrane is reduced to a single layer of ciliated cells. The air sacs, in which the smallest tubes end, are composed of. Fig. 148—Two air sacs (b) into wliicli a broneliial tube (a) 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 Eddy, Walter Hollis, b. 1877. New York, Cincinnati [etc. ] American book Co
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