CHAPTER VII.
FOUR METHODS OF RESPIRATION.
In the consideration of the question of respiration, we must begin by considering the mechanical arrangements whereby the respiratory movements are effected.

The mechanics of respiration manifest through (1) the elastic movements of the lungs, and (2) the activities of the sides and bottom of the thoracic cavity in which the lungs are contained.

The thorax is that portion of the trunk between the neck and the abdomen, the cavity of which (known as the thoracic cavity) is occupied mainly by the lungs and heart.

It is bounded by the spinal column, the ribs with their cartilages, the breastbone, and below by the diaphragm.

It is generally spoken of as "the chest." It has been compared to a completely shut, conical box, the small end of which Is turned upward, the back of the box being formed by the spinal column, the front by the breastbone and the sides by the ribs.
The ribs are twenty-four in number, twelve on each side, and emerge from each side of the spinal column.