Elevation of lesioned palatal shelves in vitro.

Fetuses were obtained from CD-1 mice at a time estimated to be 12 h prior to vivo secondary palate closure. One of the palatal shelves of each partially dissected fetal head was lesioned in one of five ways, the other left intact to serve as control. Single transverse cuts extending the width of the shelf were made at one of three positions along the longitudinal axis of the shelf: one-third, one-half or two-thirds the shelf length estimated from the rostral edge. Some specimens were cut in two places, dividing the shelf into three equal segments. Another group received a lesion which separated the caudal third of the shelf from its maxillary connections. All specimens were cultured for 18 h. At the end of the culture period the heads were fixed, examined and the degree of elevation of each shelf piece assessed. Intact, control shelves of all preparations were elevated in the rostral two-thirds of the shelf, while the caudal third was partially elevated. Results seen in lesioned shelves depended upon both the size of the segment and the region of the shelf contained in the segment. The rostral two-thirds of the shelf, the presumptive hard palate, whether intact or in segments elevated without physical connections to neighboring shelf tissue. Thus, it is unlikely that this elevation requires a wave of contraction be transmitted from the caudal soft palate region. In contrast, the presumptive soft palate requires continuity with the rostral portions of the shelf both to maintain structural stability and to elevate.