Human Anatomy - Zinoviy Mirchuk, Maryna Mirchuk 2007

Axial Skeleton
Thorax

The thoracic cage (Fig. 3) is formed by the thoracic vertebrae, twelve pairs of Ribs, and the Sternum. It features two openings, known as the superior and inferior apertures. The space enclosed by the thoracic cage and the Diaphragm is called the thoracic cavity, which is separated from the Abdominal cavity by the diaphragm.

Changes in the volume of the thoracic cage are brought about by the contraction of the Respiratory Muscles attached to the ribs, thereby driving the processes of inspiration and expiration.

The sternum consists of three parts: the manubrium, the body, and the xiphisoid process. The superior margin of the manubrium features the jugular notch. The clavicles and 7 pairs of ribs attach to the lateral surfaces of the sternum via the clavicular and costal notches.

The ribs are curved bony plates that transition into Cartilage anteriorly. They are arranged symmetrically on either side of the thoracic vertebrae. There are 12 pairs of ribs, with one pair corresponding to each thoracic vertebra, counted from top to bottom. The top seven pairs of ribs articulate directly with the sternum and are referred to as true ribs. The cartilages of the 8th, 9th, and 10th pairs of ribs join the cartilage of the rib immediately above them to form the costal margin; these are termed false ribs. The 11th and 12th pairs of ribs end freely in the Muscles of the anterior abdominal wall, exhibit greater mobility than the others, and are known as floating ribs. The ribs articulate with the vertebrae via joints. Each rib comprises a HEAD, a neck, and a body. A costal groove runs along the inferior margin of the internal surface of the rib body, accommodating the intercostal vessels and nerve.

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Fig. 3. Thoracic cage