The pituitary

Abstract

Throughout the vertebrate series the pituitary shows a consistent pattern of development, involving two distinct components; a neurohypophysis, derived from the neural tissue of the floor of the diencephalon, and the adenohypophysis, an epithelial component originating from the epithelium of the embryonic mouth cavity. The cyclostomes diverge from the typical vertebrate pattern in that the adenohypophysial tissue develops from a naso-hypophysial anlagen, which in early ontogeny, lies immediately in front of the stomodeal depression (Fig. 3.1). In all probability, this mode of development was also shared by the fossil agnathans and was already established at the time of the agnathan—gnathostome dichotomy. Nevertheless, although by slightly different routes, both vertebrate groups have attained the same association of nervous and glandular tissue that has made possible the integration of endocrine functions and the adaptation of hormonally controlled physiological processes to changes in the external environment.