1. THE PITUITARY GLAND
69
however, the manner in which the primary capillary plexus receives its
blood supply vanes a good deal, and is very interesting because of the
question of whether or not the teleostean adenohypophysis receives blood
via a hypothalamc+hypophysial portal system such as is found in tetrapods, in which a primary capillary network in the median eminence
region (just anterior to the pituitary stalk) is intimately associated with
neurosecretory nerve endings, and blood passes from this network along
the hypophysial portal veins to the capillaries in the pars distalis (Green,
1966). This system in tetrapods is now believed to mediate hypothalamic
control of the pars distalis (see, e.g., McCann et al., 1968). There exists
an anatomical basis for similar hypothalamic control in teleosts in the
form of the terminations of neurosecretory fibers on or close to the adenohypophysial cells and on vessels of the primary longitudinal plexus (Sections 11, C and 11, E). There has, however, been considerable interest in
the question of whether, in addition, elements of a hypothalamohypophysial portal system occur in these fishes; that is, in essence,
whether any part of the adenohypophysis receives blood that has first
been exposed to neurosecretory terminals in the hypothalamus.
Since the adenohypophysis in teleosts obtains its blood from the primary longitudinal plexus in the neurohypophysis, the essential question
concerns the source of the blood in this plexus. In different fishes, the
details vary. In most cases, a paired orsingle hypophysial artery (derived
from the anterior carotid system) passes directly to the neurohypophysis without contributions from hypothalamic blood vessels. In
Hippocampus (Da Lage, 1958) and Cichhoma (Baker, 1962), other
branches from the internal carotid may first pass through the rostra1 pars
distalis before entering the primary longitudinal plexus. In most cases
blood from the carotid system via the hypophysial artery may be the only
source of the blood in the primary capillary plexus, apart from a very few
capillaries from hypothalamic vessels ( e.g., cyprinodonts, Follenius, 1961,
1965a,b; various species, Jasinski, 1961, 1962). In other species, the contribution from hypothalamic vessels may be more important, and it is
these exceptional cases that have aroused interest in the past. In Phoxinus,
a median ventral infundibular artery ( = hypophysial artery?) supplies
the ependymal floor of the infundibular recess, and just above the pituitary stalk it forms connections with a pair of ring vessels derived from
the ventral hypothalamic artery ( Barrington, 1960; Bhargava, 1966).
Bhargava disagrees with Barrington’s description of these connections
as a vascular bed, and instead he implies that they are few in number
and essentially form looplike connections between the ring vessels and
the ventral infundibular artery, the latter then passing into the neurohypophysial core to supply the central sinus which in the adult represents
69
however, the manner in which the primary capillary plexus receives its
blood supply vanes a good deal, and is very interesting because of the
question of whether or not the teleostean adenohypophysis receives blood
via a hypothalamc+hypophysial portal system such as is found in tetrapods, in which a primary capillary network in the median eminence
region (just anterior to the pituitary stalk) is intimately associated with
neurosecretory nerve endings, and blood passes from this network along
the hypophysial portal veins to the capillaries in the pars distalis (Green,
1966). This system in tetrapods is now believed to mediate hypothalamic
control of the pars distalis (see, e.g., McCann et al., 1968). There exists
an anatomical basis for similar hypothalamic control in teleosts in the
form of the terminations of neurosecretory fibers on or close to the adenohypophysial cells and on vessels of the primary longitudinal plexus (Sections 11, C and 11, E). There has, however, been considerable interest in
the question of whether, in addition, elements of a hypothalamohypophysial portal system occur in these fishes; that is, in essence,
whether any part of the adenohypophysis receives blood that has first
been exposed to neurosecretory terminals in the hypothalamus.
Since the adenohypophysis in teleosts obtains its blood from the primary longitudinal plexus in the neurohypophysis, the essential question
concerns the source of the blood in this plexus. In different fishes, the
details vary. In most cases, a paired orsingle hypophysial artery (derived
from the anterior carotid system) passes directly to the neurohypophysis without contributions from hypothalamic blood vessels. In
Hippocampus (Da Lage, 1958) and Cichhoma (Baker, 1962), other
branches from the internal carotid may first pass through the rostra1 pars
distalis before entering the primary longitudinal plexus. In most cases
blood from the carotid system via the hypophysial artery may be the only
source of the blood in the primary capillary plexus, apart from a very few
capillaries from hypothalamic vessels ( e.g., cyprinodonts, Follenius, 1961,
1965a,b; various species, Jasinski, 1961, 1962). In other species, the contribution from hypothalamic vessels may be more important, and it is
these exceptional cases that have aroused interest in the past. In Phoxinus,
a median ventral infundibular artery ( = hypophysial artery?) supplies
the ependymal floor of the infundibular recess, and just above the pituitary stalk it forms connections with a pair of ring vessels derived from
the ventral hypothalamic artery ( Barrington, 1960; Bhargava, 1966).
Bhargava disagrees with Barrington’s description of these connections
as a vascular bed, and instead he implies that they are few in number
and essentially form looplike connections between the ring vessels and
the ventral infundibular artery, the latter then passing into the neurohypophysial core to supply the central sinus which in the adult represents