Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 6 On the Eight Bones of the Head and the Sutures Connecting Them

Appendix A: Why the entire brain is surrounded by bones, and why these vary and are connected chiefly by sutures (1555 edition, pp. 31-32)

But although this helmet 125 [neurocranium et chondrocranium], making up the entire cavity in which the brain is contained, did not for any reason need to be constructed of various bones articulated together and capable of voluntary movement, nevertheless it consists of eight distinct bones 126 which are bound together by a structure of sutures [suturae cranii] or other strong and quite immovable, tenacious fabric [synchondroses cranii]; they are attached besides to the twelve bones 127 of the upper maxilla [viscerocranium], and together with them make up the skull [cranium] as occurs in cemeteries. Because that helmet is necessarily quite [differently] formed in different places, and since it was fitting that its osseous substance and nature vary significantly in hardness and thickness, in its depressions and processes, and in the fashioning of its great internal cavities, it could not be fashioned all of a single bone — not to mention that we commonly believe it is less exposed to injuries if constructed of several parts, since fractures and several other kinds of damage end with the bones themselves and do not go through the whole helmet like cracks in clay vases. Moreover, this crowded structure // 1555 p. 32 // of bones is conducive to the purgation of vaporous and smoky wastes; especially because the head resembles the roof of a warm house, 128 receiving wastes which rise upward and accordingly requiring greater ventilation, it was necessary that a hard and solid substance of bones, not full of holes inside and out, having no little foramina like sponge or pumice and consequently quite weak and excessively rough and harsh to neighboring parts, that such a substance provide an exit somewhere for this waste. This is provided by the various sutures of the bones. But this helmet or calvarium possesed sutures not only for the reasons mentioned but also particularly for the transit of those membranous fibers which attach the hard membrane [dura mater cranialis] of the brain to the skull itself 129 outside the ambit of certain vessels; and by the presence and benefit of the skull the fibers quite nicely (as we shall explain in the seventh book) support and, as if suspending it, preserve the cerebrum, which would otherwise collapse because of its softness and crush its own ventricles and cavities. Consequently we believe that the sutures are provided chiefly because of the hard membrane of the brain, and for the fibers that pass through the sutures and when widened and unfolded make up the membrane 130 that covers the skull on the outside, and that the sutures are distributed in accordance with the shape of the brain, which imitates the cavity of the bones of the head. Because, therefore, the oblong body is appropriately sustained along its length by fastenings and attachments 131 as well as by transverse tensions, and is held as if in suspension, the shape of the head that is called natural has in the first place three sutures. 132



Book One -- The things that sustain and support the entire body, and what braces and attaches them all. [the bones and the ligaments that interconnect them] | Chapter 6 On the Eight Bones of the Head and the Sutures Connecting Them