OVERVIEW OF THE BONT THORAX 

The bony thorax is a cone-shaped cage formed by the sternum, the costal cartilages, the 12 pairs of ribs, and the bodies of the 12 thoracic vertebrae. The thorax contains and protects the heart, lungs, and great vessels. It serves for the attachment of muscles and acts as a mechanical agent in the breathing process. The shape and mobility of the ribs make possible the enlargement of the thoracic cavity when they are elevated. The bony thorax, together with the intercostal muscles, plays an important part in respiration.

THE STERNUM

Parts of the Sternum

The sternum, or breastbone, is an elongated, flattened bone situated in the median line in the front of the chest. It consists of three parts, named: from top to bottom, the manubrium, the body or gladiolus, and the ensiform process or xiphoid process. The superior border of the manubrium presents three notches, the middle jugular or manubrial notch and two lateral clavicular notches for the reception of the sternal ends of the clavicles. The inferior border of the manubrium articulates with the superior border of the body of the sternum, forming an angle (called the sternal angle or angle of Louis) that may be readily palpated. The sternal angle marks the position of the second ribs, as well as the junction of the manubrium, and the body of the sternum. The ensiform process, or xiphoid process, the smallest of the three parts, varies much in form: it may be partly or wholly cartilaginous, perforated by a foramen, broad and thin, pointed, bifid, deflected considerably to one side or another, or inverted.

Articulations of the Sternum

The sternum articulates on either side with the clavicle at the clavicular notch and with the upper seven costal cartilages at the costal notches on the lateral border of the manubrium and the body.

THE RIBS

There are 12 pairs of ribs. They are numbered from above downward as the first, second, third, and so forth., and as the right or the left. The 1st, 11th, and 12th ribs articulate posteriorly with the body of the corresponding vertebrae, while the remaining ribs articulate with the corresponding vertebrae as well as with the vertebrae immediately above. The first seven pairs are the true (sternal) ribs; their anterior extremities articulate with the sternum by means of the costal cartilages. The remaining five pairs are the false (asternal) ribs; they are not connected directly to the sternum. The 8th, 9th, and 10th ribs have their cartilages attached to the cartilage of the rib above and are called the vertebrochondral ribs. The 11th and 12th ribs are free at their anterior extremities and are floating (vertebral) ribs.

A typical rib possesses the following common characteristics.

1. A vertebral extremity that presents for examination a head that articulates with the superior demifacet of the corresponding vertebra and the inferior demifacet of the vertebra above a short constricted part called the neck, and a tubercle, consisting of a medial articular portion and a lateral nonarticular portion. The articular portion is for articulation with the costal facet on the transverse process of the corresponding thoracic vertebra. The nonarticular portion is for the attachment of ligaments.
2. A body or shaft, the long, flattened, curved part of the rib is marked by an angle and a costal groove.
3. An oval pit into which the costal cartilage is received marks a flattened sternal extremity.

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