70
J. N. BALL AND BRIDGET I. BAKER
the primary longitudinal plexus. Barrington ( 1960) has described
CAH + ve neurosecretory cells lying in the ventral hypothalamus in close
association with the capillary connections (“vascular bed”) and drew
attention to a resemblance to the tetrapod median eminence, but Bhargava (19sS) finds that these cells, which occupy the region where the
NLT is found in other species, are not in fact particularly close to the
capillary loops. Pending further investigations, there seems no good reason to think that Phoxinus exhibits any kind of rudimentary portal system.
Another slightly unusual arrangement exists in the bitterling, Rhodeus,
in which the hypophysial artery breaks up into a superficial capillary network (rete mirabile) on the anterior face of the pituitary stalk (hypothalamic floor), from which arise the capillaries which form the primary
longitudinal plexus in the neurohypophysial core. This rete mirabile is
totally superficial and not associated with any special nerve endings such
as characterize the tetrapod median eminence (Bretschneider and de
Wit, 1947; Follenius, 1961, 1965a,b). In Cotydoru (Miller, 1944) and
Cichlasomu (Baker, 1962) meningeal vessels drain into the primary longitudinal plexus, and these receive contributions from capillaries in the
hypothalamus which in Cichhomu are closely associated with scattered
hypothalamic cells containing discrete AF + ve droplets. In Chunna
punctutus, all the blood in the pituitary is said to derive from vessels in
the hypothalamus, but no details are available about possible neurosecretory associations with these hypothalamic vessels ( Belsare, 1965).
While these scattered observations might be interpreted as indicating
some kind of portal connection between hypothalamus and adenohypophysis, the important point to emphasize is that in no teleost has any
close association between hypothalamic neurosecretory nerve endings
and blood capillaries been observed outside the pituitary itself; thus,
whether or not these various hypothalamic capillary contributions to
pituitary vascularization represent, as it were, a foreshadowing (or
reminiscence) of the portal condition, there is no reason to regard them
as functional teleostean portal systems. One must agree with Follenius
(1965a,b) that insofar as there may be a vascular link between hypothalamic neurosecretion and adenohypophysial cells in teleosts, that link
is more likely to be found in the secondary centrifugal plexus rather than
in the extrapituitary vessels supplying the primary longitudinal plexus;
this matter is considered in the next section.
E. Hypothalamic Control of the Adenohypophysis
In Section 11, B the limited information available about the behavior
of the teleostean adenohypophysis when deprived of direct hypothalamic
J. N. BALL AND BRIDGET I. BAKER
the primary longitudinal plexus. Barrington ( 1960) has described
CAH + ve neurosecretory cells lying in the ventral hypothalamus in close
association with the capillary connections (“vascular bed”) and drew
attention to a resemblance to the tetrapod median eminence, but Bhargava (19sS) finds that these cells, which occupy the region where the
NLT is found in other species, are not in fact particularly close to the
capillary loops. Pending further investigations, there seems no good reason to think that Phoxinus exhibits any kind of rudimentary portal system.
Another slightly unusual arrangement exists in the bitterling, Rhodeus,
in which the hypophysial artery breaks up into a superficial capillary network (rete mirabile) on the anterior face of the pituitary stalk (hypothalamic floor), from which arise the capillaries which form the primary
longitudinal plexus in the neurohypophysial core. This rete mirabile is
totally superficial and not associated with any special nerve endings such
as characterize the tetrapod median eminence (Bretschneider and de
Wit, 1947; Follenius, 1961, 1965a,b). In Cotydoru (Miller, 1944) and
Cichlasomu (Baker, 1962) meningeal vessels drain into the primary longitudinal plexus, and these receive contributions from capillaries in the
hypothalamus which in Cichhomu are closely associated with scattered
hypothalamic cells containing discrete AF + ve droplets. In Chunna
punctutus, all the blood in the pituitary is said to derive from vessels in
the hypothalamus, but no details are available about possible neurosecretory associations with these hypothalamic vessels ( Belsare, 1965).
While these scattered observations might be interpreted as indicating
some kind of portal connection between hypothalamus and adenohypophysis, the important point to emphasize is that in no teleost has any
close association between hypothalamic neurosecretory nerve endings
and blood capillaries been observed outside the pituitary itself; thus,
whether or not these various hypothalamic capillary contributions to
pituitary vascularization represent, as it were, a foreshadowing (or
reminiscence) of the portal condition, there is no reason to regard them
as functional teleostean portal systems. One must agree with Follenius
(1965a,b) that insofar as there may be a vascular link between hypothalamic neurosecretion and adenohypophysial cells in teleosts, that link
is more likely to be found in the secondary centrifugal plexus rather than
in the extrapituitary vessels supplying the primary longitudinal plexus;
this matter is considered in the next section.
E. Hypothalamic Control of the Adenohypophysis
In Section 11, B the limited information available about the behavior
of the teleostean adenohypophysis when deprived of direct hypothalamic