Human Anatomy/Osteology/Thorax

The thorax (commonly referred to as the chest) is superior to the abdomen and pelvis and anterior to the back.

The Bones of the Thorax
The thorax is made up of 12 ribs (on each side) and the sternum (the breast bone).

Ribs
The ribs are numbered I-XII starting at the top. They all attach to the thoracic vertebrae of the same number. The ribs slant down as they progress from the posterior to the anterior of the body with their respective cartilages slanting up to meet up with the sternum. Costa is the word used to refer to a rib and its cartilage together.

The first seven ribs are called true ribs because they connect directly to the sternum. Ribs VIII through X are false ribs; they only indirectly attach to the sternum through the 7th rib's cartilage. The last two ribs are not associated with the sternum at all and are called floating ribs. The cartilage that attaches the ribs to the sternum is called costal cartilage and is composed of hyaline cartilage.

Ribs articulate with an intervertebral disk and body of the cervical vertebrae. The section of the rib which articulates is called the head. After the head of the rib comes the neck, tubercle, angle, and body (sometimes referred to as the shaft) of the rib. The under side of the rib has a costal groove which provides space and protection for intercostal nerves and blood vessels.

The space between ribs is knows as the intercostal space. This space (along with the costal cartilage) gives the rib cage enough flexibility to allow for breathing. The space also provides room for the intracostal muscles which aide in breathing.

Sternum
The sternum is a flat, spear-shaped bone in the midline of thorax. It is found on the anterior of the body. The sternum is composed of the manubrium (superior), body, and xiphoid process (inferior).

The manubrium is roughly half the length of the body of the sternum. The superior aspect of the manubrium has a slight curvature called the suprasternal notch. The clavicles (of the upper appendicular skeleton) attach laterally to the manubrium. This joint is called the sternoclavicular joint. It is also the only point where the pectoral girdle attaches to the axial skeleton. The inferior aspect of the manubrium has the manubriosternal joint, a movable joint that joins the manubrium to the body of the sternum.

The xiphoid process attaches to the sternum via the xiphisternal joint. It is the smallest part of the sternum and can vary in shape and size depending on the individual. Because it is so small, it is fragile and can easily be broke during chest compressions if they are not done correctly. In most people, the xiphoid process remains cartilaginous until the middle ages. It serves as a point of insertion for abdominal muscles and ligaments.