The structure of the roof of the fourth ventricle in pigeon and chick brains by light and electron microscopy.

The hindbrains and meninges of the pigeon and chick have been examined by light and electron microscopy. Serial section histology of the skull with the brain and meninges intact has shown that the caudal end of the roof of the fourth ventricle consists of an extensive membranous pouch which projects caudally and dorsally into the subarachnoid space. Electron microscopy of selected areas of the membranous pouch in pigeon has shown it to consist of two components: ependymal cells and pial tissue. The membrane ependymal cells are squamous, adjacent cells being linked by intermediate junctions. At the junction with the surface of the medulla the ependymal cells are continuous with the ventricular ependyma, and at the choroid plexus they are continuous with the choroid plexus epithelium. These results are discussed in relation to the fluid spaces in and around the hindbrain.