Bilateral oal thickenings of the surface ectoderm, called nasal placodes, then deelop on each side of the inferior part of the frontonasal prominence.

外胚层表面呈双边卵圆形增厚形，发展为额的下半部分。

The origin of flaps was frontonasal flap in 58 cases, bilobed flap in 67 cases, reforming rhomboid flap in 152 cases, nasolabial flap in 118 cses, forehead falp in 33 cases.

皮瓣来源于额皮瓣58例，双叶皮瓣67例，改良菱形皮瓣152例，唇沟皮瓣118例，额正中皮瓣33例。