ABSTRACT
In the golden hamster the critical days of palatal development occur between days 12 and 14 of gestation. During this period the shelves undergo transposition from vertical positions alongside the tongue to horizontal positions above it, and undergo fusion with each other. Palatal transposition, per se, probably takes place on or about day 12. Present data are in-sufficientto indicate in which direction this occurs. Although epithelial remnants arestill present in the midline of the palate on day 13, they have completely disappeared by day 14, thus signaling the completion of the fusion process. Preosteoblast areas are clearly visible on day 12 but actual ossification is first seen on day 13.
Cadmium apparently has a marked deleterious affect on the head mesoderm of golden hamsters, causing the production of numerous malformations, including unilateral and bilateral cleft lips and palates. It is suggested that the clefts found in cadmium-treated hamsters are due to a mesodermal deficiency rather than to a delay in shelf transposition. Marked abnormalities in cartilage formation and delays in ossification are also described.
The mechanism of action of cadmium—whether directly on the differentiating embryonic tissue, or indirectly through action on the maternal tissues—remains to be elucidated.
