第咽囊 第2咽囊 第3咽囊 第4咽囊 第5咽囊 branchial pouch loutpocketings of endoderm of primitive pharynx /opposed to branchial groove branchial membrane: the thin membrane between branchial groove and branchial pouch---branchial pouch: /outpocketings of endoderm of primitive pharynx /opposed to branchial groove ---branchial membrane: the thin membrane between branchial groove and branchial pouch