Abstract
The developmental pattern of inner surface structures of the fundic part of the bovine abomasum was studied in association with the formation of gastric pits and glands by scanning electron microscopy and by reconstructed models. In the inner surface of the abomasum, Plicae spirales abomasi were already formed as wavy spiral folds which had many fine wrinkles (1.5-2 months of fetal age). Thereafter, the surface of the folds tended to be split into many straight longitudinal ridges (3-4 months of fetal age). On each straight ridge, shallow constrictions appeared from place to place and were increased in number, eventually subdividing the ridge into independent swellings. The lamina propria showed the honeycomb-like networks, among which deep holes were formed (4-5 months of fetal age). The subdivided swellings of the ridges were progressively complicated in shape, appearing as well-defined, sandbag-like hillocks. Then, these hillocks turned to be slender and shaped irregularly, probably owing to the numerical increase of hillocks. The honeycomb-like networks of the lamina propria became finer than before (5-7 months of fetal age). The hillocks were gradually lengthened and thickened, and appeared to be gradually swollen and approached to each other in various manners. In some cases, four hillocks were fused to make a quadrilateral framework, in the center of which a deep hollow was left. In some other cases, two or three hillocks were oppressed and disappeared, just leaving deep hollows here and there (7-9 months of fetal age and neonatal age).
