Vascularization of the pituitary of the Australian lungfish and Neoceratodus forsteri

The vascularization of the brain and the pituitary region of the Australian lungfish, Neoceratodus forsteri is described from serial section reconstru ction. The distal lobe has no direct arterial blood supply and receives blo od solely from a pituitary portal system basically similar to that of other sarcopterygians. The primary capillary plexus of the median eminence recei ves its arterial blood from the infundibular arteries, which on their way d istribute some small branches to the prechiasmatic region. The primary plex us also receives capillaries from the adjacent pial hypothalamic plexus. Th e primary capillary plexus of the median eminence comprises a rostral 'unco vered' and caudal 'covered' part which are not sharply delineated. Distinct portal vessels connect the 'uncovered' rostral part of the primary plexus with the secondary capillary plexus supplying the rostral subdivision of th e pars distalis. The 'covered' caudal part of the primary plexus merges int o the proximal subdivision of the pars distalis, apparently without formati on of distinct portal vessels. The primary plexus has some connections with the plexus intermedius via a hypophysial stem capillary plexus. The plexus intermedius has a substantial arterial supply and gives off capillaries to the parenchyma of the pars intermedia. The adenohypophysis is drained into an unpaired hypophysial vein. The significance of the vascular pathways is discussed from comparative, functional, and evolutionary viewpoints.