But it is not, as Galen had already pointed out (see above). Secondly, Descartes thought that the pineal gland is full of animal spirits, brought to it by many small arteries which surround it. But as Galen had already pointed out, the gland is surrounded by veins rather than arteries. Third, Descartes described these animal spirits as “a very fine wind, or rather a very lively and pure flame” (AT XI:129, CSM I:100) and as “a certain very fine air or wind” (AT XI:331, CSM I:330). He thought that they inflate the ventricles just like the sails of a ship are inflated by the wind. But as we have mentioned, a century earlier Massa had already discovered that the ventricles are filled with liquid rather than an air-like substance.