The ribs are the bony framework of the thoracic cavity. Generally, there are twelve pairs of ribs. Each rib articulates posteriorly with two thoracic vertebrae; by the costovertebral joint. An exception to this rule is that the first rib articulates with the first thoracic vertebra only. According to their attachment to the sternum, the ribs are classified into three groups: true, false, and floating ribs. The true ribs are the ribs that directly articulate with the sternum with their costal cartilages; they are the first seven ribs. The false ribs are the ribs that indirectly articulate with the sternum, as their costal cartilages connect with the seventh costal cartilage; by the costochondral joint; They are the eighth, ninth, and tenth ribs. However, the floating ribs are the ribs that do not articulate with the sternum at all; they are the distal two ribs. The true ribs articulate with the sternum by the sternocostal joints. The first rib is an exception to that rule; it is a synarthrosis. Another thing that is good to know is that the first rib could uniquely articulate with the clavicle by the costoclavicular joint.