Foundational, esoteric texts on the third eye. For centuries, the pineal gland has occupied a unique place in Western thought--at once a biological organ and a symbol of inner illumination. In the seventeenth century, René Descartes called it "the principal seat of the soul." In the late nineteenth and early twentieth centuries, esoteric philosophers reimagined it as the dormant "third eye," the organ of spiritual perception. The Pineal Gland gathers key foundational writings from this Western mystical lineage, culminating in Manly P. Hall's important writings from Man: The Grand Symbol of the Mysteries . Here, the pineal gland emerges not merely as anatomy, but as allegory--a bridge between matter and consciousness, body and spirit, seen and unseen. Curated for the modern reader, this compact volume traces how one small gland became a vast symbol of awakening, vision, and the hidden dimensions of human potential.