(Chapter 12) Footnote 18:

Vesalius’ error regarding the function of the lacrimal or tear duct reflects the ancient doctrine that the brain excretes pituita or phlegm, a byproduct of the brain’s manufacture of “animal spirit” or psychic pneuma, on which see chapter 5 n. 9 above. “According to Galen, phlegm was excreted into the nose through the cribriform plate of the ethmoid bone, but, much to the ire of Sylvius, Vesalius declares Galen in error.” — O’Malley 1964, p. 154. See Vesalius’ discussion in his description of M3. Vesalius does recognize that the primary function of the cribriform plate and foramina was “for the entry into the head of odors” via the olfactory cranial nerve endings (p. xxx above).