At S17, the mesoderm of the left and right sides of the maxillary process gives rise to the secondary palatal processes. Both processes grow firstly in a medial direction. By S18-22, they are later orientated on both sides of the tongue vertically to the mouth floor. The tongue lies in between. As the face grows, the tongue withdraws. The secondary palatal processes assume a horizontal position. They fuse together with the premaxilla and with the nasal septum.