The ultrastructure of the rhombencephalic posterior tela and adjacent tissues in an amphibian, Rana pipiens.

The posterior tela of the rhombencephalon, the overlying arachnoid mater, and the pial surface of the medulla were examined by transmission electron microscopy in the frog, Rana pipiens. The arachnoid mater and the pia mater have, with minor exceptions, similar ultrastructural characteristics to the same structures in mammals. The posterior tela, on the other hand, is an unusual membrane, the ependymal cells of which are modified to form numerous intercellular pores. These cells are pleomorphic (round, columnar or squamous) and have relatively few surface specialisations while their cytoplasm in electron-dense due to numerous microfilaments. Ependymal cells at the edges of pores are characterised by dense coils of basal lamina inserted into indentations of the lateral plasmalemma and, near the apical surface, by small specialised attachments to adjacent ependymal cells which are otherwise in a different plane.