Organogenesis
\The anterior and posterior parts of the pituitary have different embryological origins.
The ectoderm of the roof of the developing oral cavity (light color) gives rise to the adenohypophysis.
The neurohypophysis is formed by a downgrowth of neural ectoderm from the floor of the developing diencephalon.
( from Junqueira LC, Carneiro J, Basic Histology: Text & Atlas. 11th ed. New York: McGraw-Hill, Inc., 2005. )
Along the posterior part of the the anterior lobe there is a narrow region called the pars intermedia, which also has its embryological origin in Rathke's pounch. The pars intermedia is poorly developed in humans.