[Introductory]
No figure is prefixed to this chapter, because the jugal bone, marked V and X ¹ , was in the third and fifth figures of the preceding chapter; likewise, its suture [sutura temporozygomatica] was marked Z in the third figure and Y in the fifth. The bones that resemble a rock outcropping, which we call petrous, ² are also shown in the fifth figure of the preceding chapter in the whole area where C, C, M, M, M, m, m, m, m, k, ³ and such letters occur in the base of the skull.

Names are assigned to certain areas of bone as if they were entirely separate
Among the remaining bones of the body, certain bones lacking their own edges and boundaries are described by professors of dissection no differently than if they were separate bones, and are mentioned with the others in the number of bones. To this class belongs the bone named os iugale by the Latins and zu/gwma by the Greeks because both bones (there is one on each side) are compared by experts in anatomy to the yokes of cattle or horses. ⁴

The jugal bone [arcus zygomaticus]
The jugal bone — or rather the place on the skull identified by this name — consists of two bony processes meeting each other at an oblique suture. The posterior part of it (X in figs. 3 and 5, ch. 6) is a process [processus zygomaticus] of the temporal bone; the anterior (V in the same figures) is considered a process [processus temporalis] of that bone [os zygomaticum] which forms the entire outside corner of the eye socket [orbita] and will be counted the first of the bones of the upper maxilla. Accordingly the jugal bone does not have its own ends and is nothing but a region of two processes joined to each other by a suture (Z in fig. 3, ch. 6) [sutura temporozygomatica].

The use of the jugal bone
The jugal bone has no marrow, being solid, hard, and rugged as a stone. It was fitting for it to be constructed in this way (D, then G and later D in the 4th table of muscles) ⁵ because it [arcus zygomaticus] had to be placed in front of the temporal muscle like a cover; it is convex on the outside, concave in the inside, very wisely placed opposite that muscle. ⁶

How Nature made provision for the temporal muscles
Yet Nature was not at all content with this bulwark, and to a great degree hid the temporal muscle among the other bones of the head, carving a hollow [fossa temporalis] in the bones highly suitable for the reception of a muscle and hedging it about on every side by bulges and promontories of neighboring parts. Very deservedly did she construct this, because when the muscles of the temples are abused they bring on convulsions, fevers, unconsciousness, and madness, since they are near the beginning of the nerves [nervi craniales] and only bone separates them from the brain and its membranes [meninges]. Moreover, five twigs (Q, R, b, c, and d in the figure preceding chapter 2, Book 4 ⁷ ) of the cerebral nerves (besides the three known to other anatomists, I have found two more) are implanted in each muscle. ⁸ On this account it was helpful for the divine Hippocrates to pronounce that the blows most likely to bring unconsciousness are temporal. ⁹

The mansorius muscle [m. masseter] originates at the jugal bone
We shall fully pursue the pre-eminence of these muscles in Book Two with every one of the rest. There it will be explained that the jugal bone is particularly shaped so that the masseter or mansorius ¹⁰ muscle may conveniently originate from it.

The bones resembling a rocky outcropping
The bones that resemble a rock [os temporale, pars petrosa] or rocky outcropping in hardness and appearance were called liqoeidh= by the ancients ¹¹ (visible at the base of the skull in figure 5, chapter 6). The lower part of the head is like this where the dorsal medulla [medulla spinalis] descends from the skull and where the mammillary [pars petrosa, processus mastoideus] and styloid processes [facies inferior partis petrosae, processus styloideus] of the temporal bones begin. The bones of this region are the hardest and most solid of the entire body, ¹² and for the sake of convenient origins and insertions of muscles is in truth as like as can be to a rough and jutting rock. Therefore I think this a well-named part, and I believe no bone in the body bounded by its own circumference was called “rocklike” or “stony” by the ancients. ¹³ I am aware, however, that many have applied this name only to the bones of the temples — not to all of them, but that part of them that puts out the processes just mentioned. So far as I am concerned, it will be acceptable so to name the temporal bones, provided it escape no one that the region we call the base of the skull is very often called the petrous bone by anatomists, and that they sometimes mention certain bones as if they had their own circumference when in fact they can be thought nothing other than the ends of two bones that meet (as I have already said), and sometimes a single part of one bone, as you shall hear happens in the bones [osssa coxae] that fit into the sides of the sacrum (see the three figures of chapter 29) and are given one of three names [ilium, ischium, pubis] according to their location.