Men do not have one less rib than women. Both men and women have the exact same number of ribs.
The myth that men have one less rib dates back to the Biblical era. This belief is due to a Bible verse that states that God took one of Adam's ribs and used it to create a woman.
There are 24 ribs in the human body, 12 on each side. The seven top ribs are known as "true" ribs, and the three ribs below the true ribs are known as "false" ribs. The remaining two ribs are called the floating ribs.