It has been suggested that head posture changes, tongue movements and jaw opening reflexes are required to enable palatal shelf elevation to occur in normal cranio-facial development. This study presents the results of dimensional changes which take place in the oro-nasal cavity of the embryo during the time elevation of the palatal shelves takes place. It has been shown that the vertical dimension of this cavity greatly increases in size during this period of cranio-facial growth, and can be accounted for by a sagittal mandibular growth spurt and a backward rotation of the upper face. The findings therefore support the concept that rapid and orderly growth of neural, cervical and facial components of the head and neck is an essential requirement for correct palatal shelf elevation, and not mechanical forces generated by muscular activity.