1727. CONCERNING THOSE WHO CONSTITUTE THE "PIA MENINX" OF THE BRAIN. There are certain spirits not given to speaking like the former, but serving to the further development of the ideas of others, and acting also as passive forces. They are quite modest in their temperament, and are heard still higher above the head. Their common movement was a flowing one [fluidus] in a transverse direction in the brain from the front part backwards, [differing from that of] another class whose common flowing motion was transversely from one and the other temple towards the middle of the brain, so that the place of meeting should be that of the longitudinal sinus.