What is a simian crease/line?

Single palmar crease: Simian crease is a single line that goes across one's palm without a break in the crease or line. In some people this finding can be associated with down syndrome.

Single palmer crease: Most people have a split palm fold/crease that begins at the lateral palm border & turns up between the index & second finger.A second crease starts above the thumb & breaks up before reaching the lateral palm border.The simian (apelike) crease joins the two as one.It is thought to represent less muscle tone during fetal development.It occurs in both nl people & a higher # with Down syndrome