Review/ Background ● First week Buccopharynge Second Week Prenotochordal cells o Third- 8th week Primitive node X-section at"B" Primitive streak Gastrulation Cloacal membrane A primitive pit Primitive Primitive .Primitive node ● Primitive streak Epiblast Am mniobla notochord(脊索) Invaginating HypoblastReview/Background •First Week •Second Week •Third- 8th week –Gastrulation •Primitive pit •Primitive node •Primitive streak •Notochord（脊索）