The vascular pattern of the endolymphatic sac in the human embryo.

The venous vascular anatomy of the endolymphatic sac in human embryos was examined. The endolymphatic sac was found to be covered by sinusoid-like blood vessels arising from the sigmoid sinus. A rich and extensive capillary network was present on the epithelial surface of the endolymphatic sac. Connections between this capillary bed and the vein in the paravestibular canaliculus were seen. The blood of the endolymphatic sac can therefore drain either into the vein of the vestibular aqueduct in the paravestibular canaliculus or directly into the sigmoid sinus. The vessels lying on the endolymphatic sac are thin-walled and irregular. The endothelial cells lies in direct contact with the epithelial cells of the endolymphatic sac. The reduction of the dense capillary bed in the young embryo to only a few vessels in the order embryo is described.