Posted: Feb 02, 2011 11:51 pm
just quoting wiki.
from the link to a PDF there, the number can also fluctuate with the fusion of 2 (or more) or fork of the ribs, again with a slight increase in women, and seems to be mainly on the right side (the fused/forked rib has a prevalence of 0.15-0.31%, a supernumerary rib has a prevalence of 0.5%)
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.[1] Variations in the number of ribs occur. About 1 in 200-500 people have an additional cervical rib, and there is a female predominance.[2] Intrathoracic supernumerary ribs are extremely rare.[3]
from the link to a PDF there, the number can also fluctuate with the fusion of 2 (or more) or fork of the ribs, again with a slight increase in women, and seems to be mainly on the right side (the fused/forked rib has a prevalence of 0.15-0.31%, a supernumerary rib has a prevalence of 0.5%)