The pituitary is a composite gland, the anterior lobe being derived from an evagination of the stomodeal ectoderm known as Rathke's pouch, while the posterior lobe is an extension of the forebrain. The weight of the adult human gland is approximately 620mg; in women, twenty per cent, and in men, twenty-five per cent, of this gland is posterior pituitary. Nervous tissue is the principal component of the posterior pituitary. The immediate anatomical relationship of the pituitary gland with surrounding structures is seen in Fig. 5.1
