The Ribs

The ribs are flat, thin bones that, together with the sternum, make up the ribcage. The ribs provide protection for vital organs in the upper body, including the heart and lungs.  The ribs also help to protect major vessels in the upper body.  There are twelve pairs of ribs, accounting for 24 total rib bones.  The ribs are divided into the following three categories:  true ribs, false ribs, and floating ribs.  The primary differences are size, and how they connect to the front of the skeleton.  Below is a more detailed description of the three categories.

True Ribs
The first seven pairs of rib bones (beginning at the top of the sternum) are called "true ribs."  They connect to the spine (by ligaments) at the back, and connect to the sternum by costal cartilage in the front.  Costal cartilage is elastic and allows the ribcage to expand during respiration.

False Ribs
The next three pairs of rib bones (8, 9 and 10) are called "false ribs."  Like the true ribs, false ribs are connected to the spine at the back.  The primary difference in true ribs and false ribs comes in where the false ribs connect at the front.  Instead of connecting to the sternum, false ribs (which are also slightly shorter than true ribs) actually connect to the lowest true ribs (this may be observed in the picture, above).

Floating Ribs
The last two pairs of ribs (11 and 12) are the smallest of all of the rib bones, and are called "floating ribs."  They get the name "floating rib" because they are connected to the spin at the back, but are not connected to anything at the front, thus appearing to "float."

In addition to protecting vital organs, such as the heart and lungs, the ribs serve other important purposes in the human body.  The ribs give shape and support to the chest.  They protect parts of other organs, including the stomach, spleen and kidneys.  The ribs also help humans to breathe.  The cartilage that connects the true ribs to the sternum allows the chest to expand when you inhale and the lungs fill with air.  The rigidity and mass of the rib bones then help to contract the lungs and expel air when you exhale.