From Academic Kids
In anatomy, the ribs (Latin costae) are the long curved bones which form the rib cage. They surround the chest (Latin thorax) of land vertebrates. They protect the lungs, heart, and other internal organs of the thoracic cavity.
In mammals, obvious ribs only occur in the chest: fused-on remnants of ribs can be traced in development in neck vertebrae and sacral vertebrae. In reptiles, ribs sometimes occur in all vertebrae from the neck to the sacrum.
In fish, the full set is four ribs on each vertebra. This can easily be seen in the herring. Not all fish have the full set.
The human skeleton has 24 ribs, 12 on each side. (A small proportion have one pair more or fewer). They are attached to the vertebral column behind. The first seven pairs are connected to the sternum in front and are known as true ribs (costae verae, I-VII). The eighth, ninth, and tenth are attached in front to the cartilaginous portion of the next rib above and are known as false ribs (costae spuriae, VIII-X). The lower two, that is the eleventh and twelfth, are not attached in front and are called floating ribs (costae fluitantes, XI-XII). The spaces between the ribs are known as intercostal spaces; they contain the intercostal muscles, nerves, and arteries. The rib cage allows for breathing due to its elasticity. In some humans, the rib remnant of the 7th neck vertebra on one or both sides is replaced by a free extra rib called a cervical rib, which can cause trouble for the nerves going to the arm.