Figure 1. ‘The whole brain is nothing but a tissue constituted in a particular way’. Illustration of the brain as a ‘net or mesh’, with the pineal gland (H) in the centre, from the first French edition of Descartes’ L'homme.

Figure 2. Descartes’ conception of reflex action. The stimulus A pulls the nerve fibre at B and thus opens the entrance to a particular pore in the brain, allowing the influx of the animal spirits into the nerves and leading to immediate muscular motion. The oval ‘cavity’ in the brain labelled F is not the pineal gland but the ventricle. From L'homme.

Figure 3. Descartes’ analogy for associative memory. Just as the repeated passage of needles through a linen cloth leaves traces, so certain ‘passageways’ in the brain are altered in perceptual experience, and thus ‘become more apt than the others to be opened in the same way when the [animal] spirits again flow towards them’. From L'homme.