Cerebral aqueduct ( AQ ; His 1895 ) : The part of the ventricles (Hippocrates) in the median plane (Henle, 1855) of the midbrain (Baer, 1837), continuous rostrally (Schulze, 1893) with the third ventricle (Galen, c173) and caudally (Cleland, 1879) with the fourth ventricle (Galen, c177). Vesalius (1543; see translation by Singer , 1952, p. 36; also see May, 1968, pp. 420-423) first clearly described it in macrodissected adult humans, Aranzi (1587, p. 549) first called it an aqueduct, and His (1895, p. 83) called it the cerebral aqueduct for macrodissected adult humans.