DefinitionA simian crease is a single line that runs across the palm of the hand. People normally have three creases in their palms.The term "simian crease" is not used much anymore since it tends to have a negative meaning (it refers to monkey or ape). The crease is usually just referred to as a single palmar crease.Alternative NamesSingle palmar crease; Transverse palmar crease; Palmar creaseConsiderationsStrong lines (called palmar flexion creases) appear on the palms of the hands and soles of the feet. The palm normally has three of these creases. But sometimes, the horizontal creases join together to form a single one.Palmar creases develop while the baby is growing in the womb, usually by the 12th week of gestation.A single palmar crease appears in approximately 1 out of 30 people. M