(Chapter 38) Footnote 7:

So-called because in pigs the thyroid cartilage resembles a door (Gk. thyra). Though Vesalius discusses the thyroid cartilages of cattle and pigs and notes that the human cartilage is differently shaped, he does not note that the accepted Greek term is a misnomer with respect to human anatomy. See May 1968 p. 352 n. 32.