THIRD AND FOURTH VENTRICLES, AQUEDUCT OF THE MID BRAIN, AND PINEAL GLAND.

If you now repeat the movement of that body [the vermis] which covers the passage and, simultaneously with this movement, you raise it upwards somewhat, then you can see the end of the passage which opens out into the posterior ventricle. This is closed up and covered in by the vermiform process [vermis inferior] which, from behind, forms a sort of lid for it [the ventricle] as soon as you draw back the whole of the body which covers the passage towards the rear, and it [the ventricle] opens itself as soon as this body goes forwards. This is the moment to introduce from in front into the posterior ventricle whatever smooth cylindrical instrument you have available, the calibre of which corresponds to the opening of the passage, whether now the instrument be made of wood, copper, iron, silver or gold. Should it be of wood, then it should be first and foremost of boxwood, since this wood is strong and very smooth. The Greeks are accustomed to name all instruments of such use with the generic term sounds. For my part, I have sometimes in the past, when I had no other thing at hand, inserted into this passage from the middle ventricle the writing reed, though I did not introduce the tapered end with which one writes, for this is sharp, but the other rounded-off end, and I pressed it steadily and gradually onwards, until I brought it into the posterior ventricle without boring through any part of the surroundings. Do you now turn your attention to and consider particularly what I am about to describe for you.