The two lungs are the essential organs of respiration; the right lung has three lobes, the left, two. The base of each lung rests upon the convex surface of the diaphragm.
FRONT VIEW OF THE HEART AND LUNGS, AND LARGE BLOOD-VESSELS.
The root of each lung is formed by the bronchus and blood-vessels, which enter the lung a little above the middle of its inner surface, and connect it to the heart and trachea. With the exception of the root, the surface of each lung is free and moves in the cavity of the thorax. The bronchus is one of two tubes which arise from the bifurcation of the trachea. It conducts the air from the trachea to either lung. The bronchial tubes are sub-divisions, or ramifications, of the bronchus and terminate in the air-cells.
MUSCLES OF RESPIRATION.
Inasmuch as voice is vocalized breath, it is important to give attention to respiration.
The principal muscles used in the ordinary movements of inspiration are:—
| I. | Diaphragm. | |
| II. | Levatores costarum. | |
| III. | External intercostals. | |