We are now ready to begin the study of the arrangement and working of the respiratory apparatus. With its consideration, we complete our view of the sources of supply to the blood, and begin our study of its purification.
Fig. 84.—The Epiglottis.
203. The Trachea, or Windpipe. If we look into the mouth of a friend, or into our own with a mirror, we see at the back part an arch which is the boundary line of the mouth proper. There is just behind this a similar limit for the back part of the nostrils. The funnel-shaped cavity beyond, into which both the mouth and the posterior nasal passages open, is called the pharynx. In its lower part are two openings; the trachea, or windpipe, in front, and the œsophagus behind.
The trachea is surmounted by a box-like structure of cartilage, about four and one-half inches long, called the larynx. The upper end of the larynx opens into the pharynx or throat, and is provided with a lid,— the epiglottis,—which closes under certain circumstances (secs. 137 and 349). The larynx contains the organ of voice, and is more fully described in [Chapter XII].
The continuation of the larynx is the trachea, a tube about three-fourths of an inch in diameter, and about four inches long. It extends downwards along the middle line of the neck, where it may readily be felt in front, below the Adam’s apple.
Fig. 85.—Larynx, Trachea, and the Bronchi. (Front view.)