Palatal closure in the mouse as demonstrated in frozen sections

During development of the secondary palate, mouth‐opening reflexes and swallowing movements have been observed previously. They have been assumed to be necessary in order to allow the descent of the tongue, thus enabling movement of the palatine shelves from a vertical position lateral to the tongue, to a horizontal position superior to the tongue. Interpretation of fixed, paraffin‐embedded sections, showing large spaces in the oral cavity, has added to the concept that the tongue descends into a space. Hexane‐quenched, cryostat‐cut, frozen sections of fetal mice heads show that no oral space exists at any time during elevation of the palatine shelves. Interpretation of static micrographs indicates that prior to shelf elevation the tongue is in contact with the nasal septum above and the vertical palatine shelves laterally. When the shelves elevate they seem to “flow” dorsally and interpose themselves between the tongue inferiorly and the nasal septum superiorly.