Crotch

Etymology
From croche:

Noun

 * 1) The area where something forks or branches, a ramification takes place.
 * ''There is a child sitting in a crotch of that tree.
 * 1) The (ventral) area of a person’s body where the legs fork from the trunk
 * Every mile they rode their crotches felt worse saddlepain.
 * 1)  Either the male or female genitalia.