The endotheliochorial interhemal membrane of the Indian musk shrew, Suncus murinus: an ultrastructural study.

Even though the chorioallantoic placenta of Suncus has been previously investigated with light and electron microscopy, controversies related to its structure still remain. To resolve these, Suncus murinus placentae from several (early and late limb bud, advanced pregnancy, and full term) were examined by electron microscopy. The interhemal membrane of Suncus comprises a maternal endothelium with basal lamina, syncytial trophoblast with its basal lamina, fetal mesenchyme, and fetal capillary endothelium. Layering of these components remain unchanged throughout gestation. The most striking feature of the interhemal membrane is the hypertrophied mesenchymal and maternal epithelial layers. The syncytiotrophoblast develops into a sieve-like transtrophoblastic spongy layer bearing numerous processes of the hypertrophied maternal endothelium. Mesenchymal cells intervene amidst the fetal endothelium displaying a high protein synthesizing activity. The interhemal membrane of Suncus is confirmed to be endotheliochorial.