Your pituitary gland is about the size of a pea and is situated in a bony hollow, just behind the bridge of your nose. It is attached to the base of your brain by a thin stalk.

The hypothalamus, which controls the pituitary by sending messages, is situated immediately above the pituitary gland. The optic chiasma, or 'optic chiasm', is the part of the brain where the optic nerves partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.

More Info: en.wikipedia.org