Morphological characteristics of initial lymphatics in the tongue as shown by scanning electron microscopy.

The subepithelial lymphatics of the rat tongue were examined by scanning electron microscopy in interstitially fixed tissue and corrosion casts. In tissue preparations fixed at low interstitial pressures, the endothelium exhibits broad and flat cells with serrate endothelial borders. In the course of the intercellular border system, simple junctions and overlapping zones occur. The latter have the appearance of pocketings. In tissue fixed at high interstitial pressures of up to 75 mm Hg, many endothelial cells become bulged and show long or short processes. The pocketings disappear and are replaced by openings which are covered by a fine fibrous network surrounding the vascular wall. The plexus-like arrangement of the subepithelial lymphatics of the tongue can well be demonstrated in corrosion casts. The vascular system consists for the most part of capillary vessels anastomosing like a net or terminating blindly in rootlets. The imprints of endothelial nuclei and cellular borders as well as of valve patterns in the casts enable a good differentiation between vascular and interstitial structures. The findings on the special morphological characteristics of the initial lymphatics are also discussed under functional aspects.