The Human Figures, &c.

The tools of work, namely the nerves, tubes, and motion threads that begin from the marrow of the brain, as rightly noted, must admit that this feeling is at least somewhat demonstrable. Mr. Descartes, who was the first of consistent thoughts, speaks so clearly on this that we have nothing special to add. The reason, he says, why the pineal gland, or so-called pine cone gland positioned above the cavities of the brain, should be considered the primary seat of the soul, in our opinion, is this: we find that all the working tools of our senses are double, like two eyes to see, two ears to hear, two hands to feel, and so forth; and that we do not have more than a single thought of the same thing at the same time, necessitating a place where the two images entering through the eyes or the two other impressions coming from some other object through the dual tools of other senses meet jointly, before reaching the soul, to prevent showing them as two causes instead of one. And one must understand that these impressions, with the help of the spirits that fill the cavities of the brain, unite in this gland; and that there is no other place in the entire body, thus they can be united there. This gland then being the primary seat, are to be understood as positioned between the cavities of the brain containing the living spirits, so that it can be moved in such diverse ways as there are perceivable diversities in the objects.

Translation Notes:
The word "Ziel" is translated as "soul" in contemporary English, a concept familiar in this context as it traditionally represents the non-physical essence of a person.
The "pineal gland" was historically considered in philosophy and anatomy to be the 'seat of the soul' due to its central position in the brain.