Cross-section of the head: scalp, skull and brain layers
A lettered key names each layer from the hair down to the foundation bone
A schematic section through the head is drawn at the upper right, with long wavy hair falling to one side. A lettered key (a to s) names each successive layer inward, from the hair, scalp and muscular flesh, through the cranium, the dura and pia mater, the brain, the rete mirabile and the foundation bone. A separate note in red chalk observes that the blow comes before the motion it causes, and that the blow has done its office once the struck thing has fled.
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Lettered section through the layers of the head
The section is keyed with letters naming each layer of the head from outside inward: a the hair, n the scalp skin, c the muscular flesh, m the thick membrane, o the cranium (bone), b the dura mater, d the pia mater, f the brain, r the pia mater beneath, t the dura mater, l the rete mirabile and s the foundation bone.
The blow precedes the motion it causes
A red-chalk aphorism notes that because the blow comes before the motion caused by it, the blow has already done its office once the struck thing has fled away.