Manly P. Hall 
The Pineal Gland [EPUB ebook] 
The Eye Of God

Scientists refer to the pineal gland as the 'atrophied third eye.’ Indeed, it, along with the pituitary, is the third eye chakra or energy center, but are more dormant than atrophied. According to Max Heindel’s, in the distant past, man was in touch with the inner worlds through an activated pineal and pituitary gland. Considered the most powerful and highest source of ethereal energy available to humans, the third eye has always been important in initiating psychic powers (e.g. clairvoyance and seeing auras). Manly traces the historical significance of the gland and its spiritual value.