Three-dimensional architecture of the subepithelial connective tissue in the omasal laminae of sheep and cattle.

The three-dimensional architecture of the subepithelial connective tissue in the omasal laminae of sheep and cattle was studied by scanning electron microscopy after treatment with 2 N NaOH solution. The omasal laminae were equipped with highly undulated subepithelial connective tissue showing various projections or ridges. In the sheep, the subepithelial connective tissue in the omasal papillae formed flat papillary projections in the oral and middle regions of the laminae. Ridges were arranged in cellular or rosette-like form in the aboral region. In the interpapillary space, the subepithelial connective tissue formed papillary projections in the oral region, parallel ridges with dentate projections in the middle region and smooth low ridges in the aboral region. In the cattle, the projections of the subepithelial connective tissue were more developed than in the sheep. The reticular or cellular ridges were uniformly arranged. The omasal papillae with horny tips located near the reticulo-omasal orifice showed various shapes of papillary projections. In the interpapillary space, round-edged and complex folded ridges with high undulations and deep grooves were observed. These findings may indicate regional and interspecies diversities in the function of the omasal mucosa.