Figure 2.9. Open human skull with dura intact (left) and with dura peeled
back (right), from Andreas Vesalius’s De Humani Corporis Fabrica (1543).
If the hard protection of the bony skull is removed (Fig. 2.9, left),
one sees covering the brain a skin-like sheet of tissue called the dura
mater, from the Latin words meaning “hard or tough mother.” This
can be peeled away (Fig. 2.9, right) to reveal another, much more
delicate layer of tissue covering the brain—the arachnoid, from the
Latin meaning “like a spider web.” Beneath the arachnoid tissue and
closest to the brain is a third delicate layer called the pia mater, Latin
for “soft or tender mother.” Between the arachnoid and pia layers is
the subarachnoid space. This space contains the cerebrospinal fluid, a
liquid that cushions the brain inside the skull and transports soluble
substances throughout the central nervous system. The dura, arach-
noid, and pia are collectively called the meninges. If the meninges be-
comes inflamed as a result of infection or other process, this condition
is called meningitis, an extremely serious occurrence because of its
close proximity to the brain.
Vesalius, as well as other early anatomists, noted that the brain was