Two nasal placodes develop inferiorly in a symmetrical fashion.
Nasal pits divide the placodes into medial and lateral nasal processes.
Inferior to the nasal complex, the stomodeum, or future mouth, forms. A nasobuccal membrane separates the oral cavity inferiorly from the nasal cavity superiorly. As the olfactory pits deepen, the choanae are formed. Primitive choanae form initially, but with continued posterior development, the secondary or permanent choanae develop. By 10 weeks, differentiation into muscle, cartilage, and bony elements occurs.