In humans, seven pairs of ribs are directly connected to the sternum, commonly known as the breast bone. The ribs that are designated one to seven are attached to the breast bone by their costal cartilages. These ribs are also referred to as "true ribs."
The thoracic cavity of the human skeletal system comprises the sternum, thoracic vertebrae and their intervertebral discs, and the ribs and their costal cartilages. The sternum is the long, flat bone located in the middle region of the chest cavity. Its basic structure includes the xiphoid process, manubrium and body. The notched manubrium is the topmost component of the sternum. Technically, the body of the sternum is called the breast bone, located below the manubrium. The xiphoid process is a small, smooth cartilagenous substance that petrifies by the time a person reaches 40 years of age.
Humans possess 24 ribs, which come in pairs that are located on each side of the body. These bony structures are flattened, elongated and slightly bent around the cavity. The ribs are generally classified into three: true ribs, false ribs and floating ribs. The true ribs are directly connected to the sternum while the false ribs, or ribs eight to 10, are indirectly attached. The floating ribs, or ribs 11 to 12, are joined to the vertebrae.