The structure of the rhombencephalic roof in the frog.

The structure of the rhombencephalic roof has been studied by serial section histology in 12 adult frogs, 3 recently metamorphosed frogs and 8 tadpoles of the species Rana temporaria. The roof of the rhombencephalon caudal to the choroid plexus consists of a delicate layer of ependyma which appears to be intact from the time of its development in the tadpole until the stage of metamorphosis. In the adult frog it is an attenuated structure displaying variable deficiencies with an apparent communication between the rhombencephalic ventricle and the surrounding subarachnoid space. The significance of this acquired communication between internal and external cerebrospinal fluid compartments in the adult frog is discussed in relationship to the classical concepts of bulk flow of the CSF in humans. Some of the limitations of these classical concepts are also discussed, and the approach to these problems by studying the comparative morphology of the CSF system in vertebrate animals is justified.