Abstract
The progressive evolution of hypothalamic centers in vertebrates is evident from examination of different vertebrates. The pattern of regulation has branched within the fishes, with the most recent fishes (teleosts) exhibiting predominantly neuroglandular control of tropic hormone release. Primitive fishes, including the chondrichthyeans, and tetrapods have specialized in neurovascular control with the development of a distinct median eminence and a hypophysial portal blood system. The distinct regionalization of tropic cell types in the fish adenohypophysis is less marked in tetrapods. The adenohypophysis of fishes is usually separable into a rostral pars distalis, a proximal pars distalis, and a pars intermedia. The pars tuberalis of tetrapods is absent in fishes but a unique ependymal structure is evident, the saccus vasculosus. Lungfishes lack both a pars tuberalis and the saccus vasculosus.
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