Anatomical observations of the development of the pituitary capsule.

A morphological study on the development of the pituitary capsule is reported, based on serial or step-sections of 56 pituitary glands from human embryos and fetuses ranging in gestational age from 4 to 40 weeks. Formation of the pituitary capsule is preceded at a very early embryonic stage by mesenchymal cell proliferation around Rathke's pouch when it forms the primitive adenohypophysis. The proportionally large adenohypophysis wraps around the neurohypophysis as it grows down from the diencephalon. Therefore, the fibrous capsule around the adenohypophysis represents the whole hypophysis as a membrane district from the dura mater or pia arachnoid membrane. The pituitary capsule appears not be to a derivative of either the dura mater or the pia arachnoid; instead it is a separate covering of the developing Rathke's pouch.