Three-dimensional structures of the connective tissue papillae of the tongue in newborn dogs.

Connective tissue papillae underlying epithelial cell layers of the lingual papillae of newborn mongrel dogs were exposed by long term hydrochloric acid treatment and observed by scanning electron microscopy. Each of the filiform papillae of ovoid shape (100-130 microns in diameter) contained a connective tissue papilla representing a smaller elliptical protrusion (90-100 microns in length, 70-80 microns in width). Its overview showed a horse-shoe shaped, opening anteriorly. Its posterior curvature projected a conical node with a rounded apex. Each of the fungiform papillae (150 microns in diameter) contained a connective tissue papilla of rounded shape (100 microns in diameter) whose upper surface was facetted with several slight depressions. The entire surface of the connective tissue papillae was found to be covered by networks of collagenous fibers of varying thickness, running in various directions. The basal surface of the epithelium revealed regularly distributed round holes that corresponded to the connective tissue papillae. In the filiform papillae, a small elliptical bulge was seen on the anterior side of each hole. Light microscope observation indicated that the anterior column of the filiform papillae contained a granular layer with moderate keratohyaline granules, whereas the posterior column did not show such a granular layer.