Structural similarities between the neurohypophyses of brook trout and tetrapods

Abstract

The vascularization and prcoptic innervation of the hypophysis of the brook trout ( Salvelinus fontinalis) indicate that the rostral neurohypophysis is structurally similar to the median eminence of tetrapods and that the caudal neurohypophysis is comparable with the neural lobe of higher vertebrates. These conclusions are supported by three observations. 1. The vascular supply to the rostral hypophysis is largely independent of that to the caudal hypophysis. 2. Neurosecretory fibers of the preoptic tract appear to terminate on a rostral capillary plexus whose extensions form the chief blood supply of the pars distalis. 3. Stainable neurosecretory material accumulates in the extremities of the caudal neurohypophyseal processes which often abut on venous channels. It is suggested that some of this material passes directly into the systemic circulation.