This brain is partially covered with the arachnoid and pial layers of the meninges.
The pia mater is the innermost of the 3 layers of meninges, which tightly covers the brain itself, conforming to its grooves and folds. This layer is rich with blood vessels that descend into the brain.
Outside the pia mater, which tightly contours the brain, is the arachnoid mater, which is a thin weblike layer. Between these 2 layers there is a space called the subarachnoid space, which contains cerebrospinal fluid. This space is where the major arteries supplying blood to the brain lie.
Subarachnoid hemorrhage is caused when a blood vessel ruptures in this space.
The combination of arterial and venous blood flowing to and from the brain, light versus dark, creativity and functionality, this just a tiny bit of the capability our brain has to offer.