During the development of the mammalian secondary palate, the lateral palatine process (the palatal shelf) rises from the vertical plane beside the tongue to the horizontal plane above it. To determine the mode of elevation of the palatal shelf, we have cultured the whole ICR mouse fetus on day 14 (0–2 h) of gestation with a scratch as a marker at the distal edge of the anterior fourth of the vertical palatal shelf. After 6–18 h of culture, the survival ratio was 78.9% and the palatal shelf rose horizontally above the tongue in 22.2% of the surviving fetuses. The scratch was found as a scar on the oral epithelium laterally to the medial edge of the elevated palatal shelf. These results indicate that the medial edge of the horizontal shelf was newly formed from the medial wall of the preceding vertical-stage shelf during elevation, and that the palatal shelf was elevated by a remodeling process in the anterior half of the sh