蔓叶线，有时又叫双蔓叶线是 Diocle 在公元前180年发现的曲线。

蔓叶线的标准曲线方程为：

其中a是常数。

In geometry, a cissoid is a curve generated from two given curves C₁, C₂ and a point O (the pole). Let L be a variable line passing through O and intersecting C₁ at P₁ and C₂ at P₂. Let P be the point on L so that OP = P₁P₂. (There are actually two such points but P is chosen so that P is in the same direction from O as P₂ is from P₁.) Then the locus of such points P is defined to be the cissoid of the curves C₁, C₂ relative to O.