Subarachnoid space ( Magendie, 1827 ) : The part of the ventricular-subarachnoid space 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; it is continuous with the ventricles (Hippocrates) and is filled with cerebrospinal fluid. The existence of fluid under the dura, in what is now called the subarachnoid space, was known to Hippocrates (see Millen & Woollam, 1962, p. 1), and named by Magendie (1827, pp. 21, 25) in a variety of macrodissected mammals.