Pineal Gland.

Pineal Gland. a rounded body about the size of a pea, of a slightly yellowish colour, situated upon the anterior pair of corpora quadrigemina, and connected with the optic thalami by two strands of nerve-fibres termed its peduncles (see BRAIN). It contains small cavities in its interior. The function of the gland has long been matter of speculation. It was regarded by Descartes as the seat of the soul. It has been recently discovered to be a developmental remnant of a third eye, the elements of which can still be distinctly traced in some of the lower vertebrata. See SPHENODON.