(Chapter 9) Footnote 1:

This illustration appears again in chapter 12 of Book I. Saunders and O’Malley believed that “the primary purpose of the illustration was to reveal that Galen had described the premaxillary bone and suture of the dog as though present in man and thus could not have been familiar with human anatomy. Vesalius thus opened a great controversy of singular importance in comparative morphology, which was to rage with bitter polemics for nearly four centuries and to be settled only in recent times. ... His discovery, from which he made the correct deduction, was one of the major factors leading to the overthrow of Galenical anatomy.” ( Saunders & O’Malley 1950, p. 58). In most vertebrates, including non-human primates, the os incisivum represents a separate element, the premaxillary bone, in the upper jaw; in the human, the premaxillary bone fuses with the maxilla by the third intra-uterine month. In the human, however, a “palatal sign” of separation between os incisivum and the rest of the maxilla may persist until the middle decades as the sutura incisiva ( Gray 1995, p. 602). O’Malley ( AVB p. 153) notes with irony that although designed to advertise a Galenic fallacy, “This very illustration convicted [Vesalius] of an error, since it displays the ethmoidal labyrinth as a separate bone, a mistake corrected some years later by Fallopio.”