The epithalamus comprises the posterior diencephalon, including parts like the third ventricle, thalamus, hypothalamus (limbic system) (HPA axis), subthalamus (HPA axis), and pituitary gland (HPA axis), habernula, stria medullaris, pineal gland, and posterior commissure. It functions to connect the limbic system to other parts of the brain. For example, it is involved with secretion of melatonin by the pineal gland and regulation of movement and emotions.