In general, the ribs move around two axes. Movement at costovertebral joints 2 to 6 about a side-to-side axis results in raising and lowering the sternal end of the rib, the "pump-handle" movement. The downward slope of the rib ensures that, in elevation, the sternum moves upward and forward, increasing the antero-posterior diameter of the thorax. Movement at costovertebral joints 7 to 10 about an antero-posterior axis results in raising and lowering the middle of the rib, the "bucket-handle" movement. In elevation, this increases the transverse diameter of the thorax.