ABSTRACT
This is a description of ultramicroscopic structures at the base of the thyroid follicle. The structural principle of the subendothelial or interfollicular space, namely basement membranes closely following both the endothelial cells of the capillaries and the epithelial cells of the thyroid, corresponds to that described by other authors in the other endocrine organs. Especially shown are small vesicle like decreases of intensity in the subendothelial space, causing bulges in both the subepithelial basement membrane and the membrane covering the endothelial cell pores thereby forming pseudopores. This membrane is in several parts a double one. The possible role played by the above mentioned structures in the basal secretion of the thyroid epithelial cell is discussed.
