The pial vessels in the Tfpi^−/−embryos were disorganized and produced glomeruloid bodies upon penetrating into the brain parenchyma. Meninges and pial vessels of E16 Tfpi^+/+ and Tfpi^−/− littermates stained for laminin. (A) The meninges of the Tfpi^+/+ brain are well organized with normal vasculature seen entering the brain parenchyma (arrow). A prominent feature of the Tfpi^−/− meninges is the large layer of abnormal vascular endothelial cells piled up in the pia mater that formed glomeruloid bodies upon entering the brain parenchyma (arrow) (scale bars, 100 µm). (B) The meningeal layers are identified by numbered brackets: (1) skeletogenous layer of the future skull, (2) dura mater, (3) arachnoid mater, (4) pia mater, and (5) brain parenchyma. Formation of the meninges was delayed in Tfpi^−/− embryos when compared with Tfpi^+/+ littermates. Vasculature was absent in the arachnoid layer of Tfpi^−/− embryos, which lacks definition of the impermeable outer layer that prevents passage of cerebrospinal fluid from the subarachnoid space (scale bars, 30 µm).