The neurohypophysis consists of three poorly defined regions: (1) the neural lobe, (2) the infundibular stem and (3) the median eminence (or part thereof1). Because of the intimate contact of the neural and the intermediate lobe in man and most laboratory animals, these two parts of the pituitary gland are frequently classed together as the posterior lobe. However, with the clarification of the development and of the secretory capacity of the neural division of the hypophysis, it becomes expedient to abandon the use of a term based purely on gross anatomic relations.
The primary structural elements of the neurohypophysis are pituicytes and unmyelinated nerve fibers. The pituicytes are derived from the ependymal cells of the neural tube and are closely related to neuroglia. They have one or more cytoplasmic processes, and frequently these end in close relation to blood vessels or connective tissue.2 The nerve fibers have their