Human rib cage:
also known as the thoracic cage, is a bony and cartilaginous structure which surrounds the thoracic (chest) cavity and supports the pectoral (shoulder) girdle, forming a core portion of the human skeleton. A typical human rib cage consists of 24 ribs, the sternum, costal cartilages, and the 12 thoracic vertebrae. It, along with the skin and associated fascia and muscles, make up the thoracic wall, and provides attachments for the muscles of the neck, thorax, upper abdomen, and back.
The human rib cage is a component of the human respiratory system. It encloses the thoracic cavity, which contains the lungs. An inhalation is accomplished when the muscular diaphragm, at the floor of the thoracic cavity, contracts and flattens, while contraction of intercostal muscles lift the rib cage up and out. These actions produce an increase in volume, and a resulting partial vacuum, or negative pressure, in the thoracic cavity, resulting in atmospheric pressure pushing air into the lungs, inflating them. An exhalation results when the diaphragm and intercostal muscles relax, and elastic recoil of the rib cage and lungs expels the air.
All ribs are attached in the back to the thoracic vertebrae.
The upper seven true ribs (costae verae, vertebrosternal ribs, I-VII). are attached in the front to the sternum by means of costal cartilage. Due to their elasticity they allow movement when inhaling and exhaling.
The 8th, 9th, and 10th ribs are called false ribs (costae spuriae, vertebrochondral ribs, VIII-X), and join with the costal cartilages of the ribs above.
The 11th and 12th ribs are known as floating ribs (costae fluitantes, vertebral ribs, XI-XII), as they do not have any anterior connection to the sternum.
The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, nerves, and arteries.
The human rib parts:
The head is the end of a rib closest to the vertebral column.
The Costovertebral joints are the articulations that connect the heads of the ribs to the thoracic vertebrae.
The neck is the flattened portion which extends lateralward from the head.
The tubercle is an eminence on the posterior surface.
The angle is a bending part.
The Costal groove is a groove between the ridge of the internal surface of the rib and the inferior border.
The atypical ribs are the 1st, 2nd, and 11th to 12th.
The first rib is a shaft that is wide and nearly horizontal and has the sharpest curve of the seven true ribs. Its head has a single facet to articulate with the first thoracic vertebra (T1). It also has two grooves for the subclavian vessels, which are separated by the scalene tubercle.
The second rib is thinner, less curved, and longer than the first rib. It has two facets to articulate with T2 and T1, and a tubercle for muscles to attach to.
The 11th to 12th ribs have only one facet on their head; the 11th and 12th ribs are short with no necks or tubercles and terminate in the abdominal wall before fusing with the costal cartilages.
Number of ribs
The number of ribs was noted by the Flemish anatomist Vesalius in his key work of anatomy De humani corporis fabrica in 1543, setting off a wave of controversy, as it was traditionally assumed from the Biblical story of Adam and Eve that men's ribs would number one fewer than women's. A small portion of people have one extra pair of ribs, or one fewer, but this is unrelated to gender.