This is the so-called c narion, or pineal gland, where in a minimized point the mind on one hand and the vital spirits on the other meet and communicate.
Mind, driven from the field of extension, erects its last fortress in the pineal gland.
In addition to these lines, all tadpoles show more or less distinctly a small whitish gland in the middle of the head between the eyes, the so-called frontal gland or pineal gland, which in early stages is connected with the brain.
The exact significance of these roots is a matter for speculation, but it seems possible that they are epiphysial structures remotely comparable with the epiphysial (pineal) complex of the craniate vertebrates.
The pineal foramen, in the parietal bones, is as constantly present as it is absent in the other orders.