Morphological study of the chorio-allantoic fetal membranes.

Morphological study of the chorio-allantoic fetal membranes has demonstrated the existence of foot processes extending from the main body of amniotic cells and containing microfibrils arranged in dense bundles as described in podocytes of renal glomerulae; on the surface fronds and between their bases many small pits and caveolae are seen; in the cytoplasm of amniotic cells large vacuoles are present; they frequently distort the nuclei into crescentic shapes. In the chorion underlying the amnios, fibroblasts and Hofbauer cells are found; their surface often has overlapping filopidal projections. The syncytium bounding the intervillous space shows a marked resemblance to that of the villi. These morphological features seem to indicate that chorio-allantoic fetal membranes might be an important route for the transporting of fluid from the maternal blood in the intervillous space into the amniotic compartment.