Thymus Gland

The thymus gland is one of the quietest organs in your body — and at the same time one of the most mysterious. It sits directly behind the breastbone, close to the heart, a small soft structure between lungs and collarbone. In childhood it is large, active, vibrant. That is where your T-cells are shaped — the immune cells that learn to distinguish between "self" and "non-self," between what belongs to you and what threatens you. That is where your immunological sense of self is formed, quite literally.