Interesting thread. It lead me to this picture and I got to wondering...This image isn't a margin drawing. It comes from the Voynich Manuscript. it kind of looks like a connection point of some kind. The woman standing in water symbolizing the synapse connection. But, it looks like only half the connection is made: Shouldn't there be a man standing in the water fountain with his arms extended into the two other tubes too?
It isn't what can be seen in the image but what isn't there. Perhaps, it's describing an inhibitor of sorts to prevent a full connection. Is this an auditory diagram or a visual one? Maybe, a connection to something else?