(Chapter 21) Footnote 30:

The Greek word means “side” as well as “rib”: see LSJ IIIa pleura/ as the side of a triangle or other figure. In Greek, the side or rib is fem. pleura/ or neut. pleuro/n. The 1555 edition omits this sentence and substitutes latus for costa in many places when referring to the sides of the scapula. Like the 1555 edition, we translate “side” to avoid confusion with the ribs that form the thorax.