CHAPTER VII. ORGANOLOGY.—Continued.
The Thoracic Cavity.
—The thorax, or chest is a bony, cartilaginous cage. It contains and protects the principle organs of respiration and circulation.
The thorax is bounded in front by the sternum and costal cartilages, behind by the twelve dorsal vertebrae and the posterior parts of the ribs, on the sides by the ribs, above by the root of the neck and below by the diaphragm.
Fig. 16—Front view of the thorax. (Gray)
In the female the thorax differs as follows from the male: Its general capacity is less, the sternum is shorter, and the upper ribs are more movable and so allow a greater enlargement of the upper part of the thorax than the male.
The capacity of the cavity of the thorax does not correspond with its apparent size externally, because, (1) the space enclosed by the lower ribs is occupied by some of the abdominal viscera; and (2) the cavity extends above the first rib into the neck. The size of the cavity of the thorax is constantly varying during life, with the movements of the ribs and diaphragm, and with the degree of distention of the abdominal viscera.
From the collapsed state of the lungs, as seen when the thorax is opened, in the dead body, it would appear as if the viscera only partly filled the cavity of the thorax, but during life there is no vacant space, that which is seen after death being filled up during life by the expanded lungs.