Fourth ventricle ( V4 ; Galen, c177 ) : The rhombic-shaped part of the ventricles (Hippocrates) in the rhombicbrain (His, 1893b), continuous rostrally (Schulze, 1893) with the cerebral aqueduct (His, 1895) and caudally (Cleland, 1879) with the central canal (Henle, 1871). The cerebrospinal fluid in the fourth ventricle communicates with cerebrospinal fluid in the subarachnoid space (Magendie, 1827) through one or more holes in the roof of the fourth ventricle. The fourth ventricle was known from macrodissected adult humans to Herophilus (335-280 BC; see von Staden, 1989, pp. 247-248), and named such by Galen (c177, c192; see translations by Duckworth, 1962, p. 19 and Singer, 1999, p. 235, respectively).