2. THE NEUROHYPOPHYSIS
169
fibers (Al, A?, and B ) terminate as a mass of rosettelike structures
on the fine intervascular channel which envelops the outer surface
of the neural processes (Knowles and Vollrath, 1966a; Leatherland et al.,
1966; Leatherland, 1967). This intervascular channel is thought to correspond to the PAS-positive “basement membrane” seen by earlier optical
methods (Follenius and Porte, 1962; Knowles and Vollrath, 1966a). At
intervals it expands to encompass capillaries within its inner space, and
it would appear to be capable of transferring neurosecretory materials to
either the pars intermedia cells on its outer side or to the capillaries
within its framework ( Knowles and Vollrath, 1966a). Jasinski (1961) has
investigated the vascular supply of the pituitary of Anguilla anguillu and
has shown that these capillaries receive their blood supply from arterioles
on the dorsal surface of the pituitary; they form a fine network over the
surface of the digitate processes of the pars nervosa, and although they
do not penetrate the relatively avascular pars intermedia, they send ramifications into the pars nervosa tissue. Similar networks of capillaries on
the surface of the neural processes, and to some extent within them, have
been seen in many other species (Ameiurms nebulosus; Palay, 1945;
Salmo irideus; Legait and Legait, 1957; Lucioperca lucioperca; Jasinski,
1962; Lebistes reticulatus; Follenius and Porte, 1962; Salvelinus fontinalis;
Hill and Henderson, 1968). In many teleosts these capillaries are closely
associated with neurosecretory terminals, and it seems reasonable to suppose that active agents are passed into them (Lebistes reticulatus; Follenius and Porte, 1962; Porichth ys notatus; Sathyanesan, 196513; Salvelinus
fontinalis; Hill and Henderson, 1968; Henderson, 1969). Follenius and
Port (1962) believe that most of the blood from the pars nervosa of
Lebistes reticulatus drains directly through the hypophysial vein into the
systemic circulation, so that active materials could reach many tissues.
However, Hill and Henderson (1968) have suggested that in Salvelinus
fontinalis capillaries of the pars nervosa drain into all regions of the
adenohypophysis, and that these vessels could carry neurohypophysial
factors which might be important in adenohypophysial control. Recently,
Henderson ( 1969) has greatly clarified the problem of the destination of
the active agents of the neurohypophysis by a detailed analysis of the
vascular supply of the pituitary of this species. She has emphasised that
the pituitary is served by two largely independent arterial supplies. The
first vascular route is well adapted to carry neurohypophysial products
from the rostral region of the pars nervosa to the rostral and proximal
divisions of the pars distalis ( adenohypophysis) , The second vascular
circuit irrigates the caudal pars nervosa, and would appear well adapted
to carry material out into the general circulation. Therefore, it is probable
that active agents could be supplied both internally to the adenohypo-
169
fibers (Al, A?, and B ) terminate as a mass of rosettelike structures
on the fine intervascular channel which envelops the outer surface
of the neural processes (Knowles and Vollrath, 1966a; Leatherland et al.,
1966; Leatherland, 1967). This intervascular channel is thought to correspond to the PAS-positive “basement membrane” seen by earlier optical
methods (Follenius and Porte, 1962; Knowles and Vollrath, 1966a). At
intervals it expands to encompass capillaries within its inner space, and
it would appear to be capable of transferring neurosecretory materials to
either the pars intermedia cells on its outer side or to the capillaries
within its framework ( Knowles and Vollrath, 1966a). Jasinski (1961) has
investigated the vascular supply of the pituitary of Anguilla anguillu and
has shown that these capillaries receive their blood supply from arterioles
on the dorsal surface of the pituitary; they form a fine network over the
surface of the digitate processes of the pars nervosa, and although they
do not penetrate the relatively avascular pars intermedia, they send ramifications into the pars nervosa tissue. Similar networks of capillaries on
the surface of the neural processes, and to some extent within them, have
been seen in many other species (Ameiurms nebulosus; Palay, 1945;
Salmo irideus; Legait and Legait, 1957; Lucioperca lucioperca; Jasinski,
1962; Lebistes reticulatus; Follenius and Porte, 1962; Salvelinus fontinalis;
Hill and Henderson, 1968). In many teleosts these capillaries are closely
associated with neurosecretory terminals, and it seems reasonable to suppose that active agents are passed into them (Lebistes reticulatus; Follenius and Porte, 1962; Porichth ys notatus; Sathyanesan, 196513; Salvelinus
fontinalis; Hill and Henderson, 1968; Henderson, 1969). Follenius and
Port (1962) believe that most of the blood from the pars nervosa of
Lebistes reticulatus drains directly through the hypophysial vein into the
systemic circulation, so that active materials could reach many tissues.
However, Hill and Henderson (1968) have suggested that in Salvelinus
fontinalis capillaries of the pars nervosa drain into all regions of the
adenohypophysis, and that these vessels could carry neurohypophysial
factors which might be important in adenohypophysial control. Recently,
Henderson ( 1969) has greatly clarified the problem of the destination of
the active agents of the neurohypophysis by a detailed analysis of the
vascular supply of the pituitary of this species. She has emphasised that
the pituitary is served by two largely independent arterial supplies. The
first vascular route is well adapted to carry neurohypophysial products
from the rostral region of the pars nervosa to the rostral and proximal
divisions of the pars distalis ( adenohypophysis) , The second vascular
circuit irrigates the caudal pars nervosa, and would appear well adapted
to carry material out into the general circulation. Therefore, it is probable
that active agents could be supplied both internally to the adenohypo-