(Chapter 6) Footnote 65:

In Renaissance orthography, the small eta may be written h or with a cursive H-shaped character easly confused with k. See Translator’s Preface. The sutures said here to resemble this letter H are (beginning at the lower portion of the coronal suture in figure 3 and moving clockwise), the coronal, squamous, sphenosquamosal, and frontosphenoid. The crossbar in this letter H is the spheno-parietal suture, in an area called the pterion, where all four bones join to make up the figure. The 1555 revision omits reference to “the natural shape of the head,” and adds parenthetically “because of its columns that slant outward at their ends,” referring to the outwardly angled ascending and descending lines of the small letterform that resembles the four sutures.