Anat. a small, somewhat cherry-shaped double structure attached by a stalk to the base of the brain and constituting the master endocrine gland affecting all hormonal functions in the body, consisting of an anterior region (anterior pituitary or adenohypophysis) that develops embryonically from the roof of the mouth and that secretes growth hormone, LH, FSH, ACTH, TSH, and MSH, a posterior region (posterior pituitary or neurohypophysis) that develops from the back of the forebrain and that secretes the hormones vasopressin and oxytocin, and an intermediate part (pars intermedia), derived from the anterior region but joined to the posterior region, that secretes the hormone MSH in lower vertebrates. Also called hypophysis. See diag. under brain.