The sea of marrow, or the brain, is one of the four seas where the marrow fluid concentrates. The essence and marrow of the body is derived from the kidney essence. It travels to the brain ventricles along the governor vessel and then gets stored in the brain. The brain is thus called the sea of marrow because of its function of storing essence and marrow. Brain marrow is the result of concentration of prenatal essence. It is further nourished by the kidney essence and essence of food and drinks after one is born. If kidney essence and the essence of food and drinks are both abundant, the sea of marrow will be nourished. Otherwise, it will be deficient.