Ventricular-subarachnoid space ( VSS ; Swanson & Bota, 2010 ) : The continuous cavity associated with the vertebrate central nervous system (Meckel, 1817) that is filled with cerebrospinal fluid (CSF). Part of the cavity is the central lumen of the vertebrate central nervous system (Meckel, 1817) that is the remnant of the embryonic lumen of the neural tube (Baer, 1837); it is referred to as the (cerebral) ventricles (Hippocrates), with walls formed by a monolayer of ependymal cells, a type of glia (Virchow, 1846). The other part is the subarachnoid space (Magendie, 1827) that lies between the outer and inner layers of meninges (Edwin Smith Surgical Papyrus, c1700 BC), the dura (Galen, c177) and pia (Galen, c192), respectively. The ventricles and subarachnoid space are continuous through holes in the roof of the fourth ventricle (Galen, c177) associated with the medulla (Winslow, 1733). The CSF is equivalent to lymph for the central nervous system and eventually drains into the venous part of the circulatory system; see Crosby et al. (1962, pp. 568-579).