Costal breathing is breathing accomplished by moving of the rib cage as a whole. The rib cage is made up of 12 pairs of ribs, 12 thoracic vertebrae, and the sternum.
Structure of a "typical" rib:
Each rib is a flat-type bone that is curved laterally. Along its inferior margin is a subcostal groove.
All 12 pairs of ribs are attached posteriorly to the thoracic vertebrae. Anteriorly, the upper 10 pairs of ribs are attached directly or indirectly to the sternum.
The indirect attachments are made through costal cartilages to the ribs above. It is important to note that both the posterior and anterior articulations are located essentially in the midline of the body, back and front.
The costal cartilages are bars of cartilage of varying lengths. Since costal cartilages are elastic, they can be twisted (deformed) and returned to their original shape.
The sternum is located in the midline anteriorly, immediately beneath the skin. The sternum is made up of three parts- the manubrium above, the body as the main portion, and the xiphoid process below.
Where the manubrium articulates with the top of the body of the sternum is a sternal angle (Louis' angle). The sternal angle is important in costal breathing, since it allows for greater expansion of the rib cage.
Thoracic Vertebrae and Segmentation:
Posteriorly, there are 12 thoracic vertebrae, joined by intervertebral discs. Their curvature, the thoracic curvature, is concave anteriorly. During breathing, this curvature straightens and thus increases the expansion of the rib cage.
The segmentation of the thorax is produced by both the intervertebral discs and the intercostal spaces between adjacent ribs. Such segmentation of the rib cage allows motion to take place, especially bending to the right or left.
The intercostal spaces are filled by two layers of intercostal muscles. The intercostal muscles extend from the vertebrae behind to the sternum in front.
A strengthening "plywood effect" is created by the arrangement of the two layers at a right angle to each other. Therefore, these muscles help to maintain the "solid-wall" condition of the thorax.
For this reason, a pressure gradient can be maintained between the inside and outside of the thorax.
Skeletal Muscles Attached to the Rib Cage:
Various skeletal muscles are attached to the rib cage. Some extend from above and draw the rib cage upward. Others extend from below and draw the cage downward.