The number of ribs was noted by the FlemishanatomistVesalius 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. (De humani corporis fabrica[1]) A small proportion of people have one pair more or fewer but this is unrelated to gender. Humans have seven rows of true ribs, each with its own connection to the sternum. Humans also have three rows of false ribs which connect to the ones above it. The last two rows, which don't connect to the sternum, are called floating ribs. In the front, the upper 7 ribs are attached 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 join with the costal cartilages of the ribs above. The 11th and 12th ribs are known as floating ribs, as they do not have any anterior connection.
Function
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.
The Costal groove is a groove between the ridge of the internal surface of the rib and the inferior border.
Types of ribs
Anterior surface of sternum and costal cartilages.
The first seven pairs of ribs are connected to the sternum in front and are known as true ribs or vertebrosternal ribs (costae verae, I-VII).
The eighth, ninth, and tenth attached in front to the cartilaginous portion of the next rib above and are known as false ribs or vertebrochondral ribs (costae spuriae, VIII-X).
The lower two, that is the eleventh and twelfth, are not attached in front and are called floating ribs or vertebral ribs (costae fluitantes, XI-XII).
In some humans, the rib remnant of the 7th cervical vertebra on one or both sides is replaced by a free extra rib called a cervical rib, which can cause problems in the nerves going to the arm.
The atypical ribs are the 1st, 2nd, and 10th 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 10th 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.
Medical conditions
Rib fractures can occur. These most frequently affect the middle ribs. When several ribs are injured, this can result in a flail chest.
