Animal physiology / by John G. M'Kendrick.

  • John Gray McKendrick
Date:
1877
Catalogue details

Licence: Public Domain Mark

Credit: Animal physiology / by John G. M'Kendrick. Source: Wellcome Collection.

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    an immense extent of internal mucous membrane, covered by vascular network, through which, as in the simpler form, the blood flows in innumerable minute streamlets, only- separated by an extremely thin membrane from the atmos- pheric air that has been inhaled; secondlythere must be such an arrangement of the circulating system, that fresh blood may be perpetually driven from the right side of the heart through the lungs, and onwards to the left side of the heart; and thirdly^ there must be arrangements for the fre- quent and regular change of the air contained in the lungs. 134. General Anatomy of the Organs.—We shall first con- sider the lungs and the passages leading to them. The back of the mouth or pharynx is connected with the outer air in two ways—namely, by the nasal passages and nostrils, and by the mouth. Through either of these channels the air may pass to and from the lungs, but the nostrils are, prop- erly speaking, the entrances to the respiratory system. Behind the root of the tongue, we find a chink or aperture, the glottis^ bounded laterally by two folds of membrane called the vocal cords, which may be more or less widely separated from each other (fig. 109). This chink or aperture is guarded by a leaf-like lid, the epiglottis, which can be closed when expedient, so as to prevent the entrance of particles of food, drink, &c. The glottis opens downwards, into a box- like chamber called the larynx (which is the organ of voice), and leading downwards from the larynx runs the trachea, or windpipe, which is kept permanently open for the pas- sage of air, by cartilaginous rings, that surround the anterior two-thirds of it. These are united, and the back of the tube is formed by a fibrous membrane or muscle. The windpipe, which is easily felt by the hand, and lies just below the pro- jecting part of the larynx, popularly known as Adam's apple, is about four and a half inches in length, and about three-fourths of an inch wide. Passing into the cavity of the chest, it divides into two branches, which are termed the right and left bronchi (fig. 76). Each bronchus enters the lung of its own side, and divides into a great number of smaller tubes, called the bronchial tubes, which again go on subdividing. These finest tubes end in elongated dilatations,
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