Morphogenesis of rabbit small intestinal mucosa.

The sequential morphologic changes of rabbit small intestinal mucosa were studied from primodial stage to birth in 86 fetuses and during the early days of life in 18 rabbit newborns. In 13-day-old fetuses, the epithelium was flat and stratified. By the 17th day, epithelial ridges were formed. The first evidence of rudimentary villus formation was noted in 20-day-old fetuses and true villi appeared by 24 days of the gestation. Intestinal glands (crypts of Lieberkühn) were first observed at 29 days. The intestine of the newborn rabbit did not possess all mucosal constituents present in the adult. The duodenal glands (Brunner's glands) appeared in the first 2 days after birth, and the muscularis mucosa, on the 5th day. The histological maturity of the intestine occurred 20 days after the rabbit was born. At all stages, the morphogenesis followed a cranio-caudal gradient developmental pattern.