(Chapter 6) Footnote 55:

Vesalius cites Historia animalium 3.7 [516a15-19 (cf. 491b2-4)] and De partibus animalium 2 [653a35]. In the first of these, distinguishing the structures of the skull, he says “The skull is not identical in all animals: in some it consists of a single bone, (e.g., the dog), in others it is composite (e.g., man), and here the female has a circular suture, whereas in the male there are three sutures which unite at the top, and are shaped like a triangle.” (Loeb trans. by A.L. Peck). In the second, Aristotle accounts for the imagined difference by explaining that larger (male) brains require more ventilation than smaller (female) brains (653b1-3).