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GRAEME CAMPBELL
cholinergic fibers. Fange has suggested that the vagi provide cholinergic
fibers to contract thc muscularis mucosae of resorptive regions, a responsc
which would tend to cause filling by decreasing the area of resorptive
epithelium exposed. He reached this conclusion because he found that
isolated preparations of the tissue were contracted by acetylcholine and
relaxed by atropine. However, he did not observe muscular contractions
of this type in response to vagal stimulation, nor did atropine treatment
affect the position of the swim bladder diaphragm in Ctenolabrus. Fange
has provided evidence for vagal cholincrgic fibers causing vasodilat a t' ion
in the secretory portion of the swim bladder. He noted that during secretion there was a marked vasodilatation in the gas gland, whereas after
vagotomy, and especially after atropine treatment, the;e was considerable vasoconstriction in the gland. But Fange rightly raised the still unresolved question of whcther the vasodilatation occurring during activity
is a primary effect caused by specifically vasodilator nerves or a secondary effect caused by the release of metabolites from cholinergically
activated secretory cells.
B. Spinal Autonomic Nerves
The sympathetic nervous system of selachians consists of a series of
paravertebral ganglia, one or more occurring per spinal nerve, linked
together at most by a loose plexus of nerve bundles. T1,ere is no compact sympathetic chain. The ganglia are connected to the spinal nerves
by white rami communicantes. Young (1933~) claims that gray rami are
absent, i.e., that there is no entry of postganglionic fibers into the spinal
nerves to reach dermal structures, but there is some evidence for sympathetic nervous control of dermal melanophores. The ganglia extend
no further caudally than the posterior end of the mesonephros in adults.
There are no cranial sympathetic ganglia nor is there any semblance of
a sympathetic chain entering the head region; however, this does not
preclude a sympathetic innervation of cranial structures via perivascular
nerve plexuses. There are no prevcrtebral ganglia, and fibers from the
paravertebral ganglia are collected into anterior, middle, and posterior
splanchnic nerves extending to the alimentary canal via plexuses on
the arterial supply. Other fibers run directly to the genital and urinary
ducts.
In teleosts, the sympathetic system has a well-defined structure resembling that found in tetrapods. Paravertebral sympathetic ganglia,
usually two per spinal segment, are linked together regularly to form
two sympathetic chains which fuse to a greater or lesser extent in differ-
GRAEME CAMPBELL
cholinergic fibers. Fange has suggested that the vagi provide cholinergic
fibers to contract thc muscularis mucosae of resorptive regions, a responsc
which would tend to cause filling by decreasing the area of resorptive
epithelium exposed. He reached this conclusion because he found that
isolated preparations of the tissue were contracted by acetylcholine and
relaxed by atropine. However, he did not observe muscular contractions
of this type in response to vagal stimulation, nor did atropine treatment
affect the position of the swim bladder diaphragm in Ctenolabrus. Fange
has provided evidence for vagal cholincrgic fibers causing vasodilat a t' ion
in the secretory portion of the swim bladder. He noted that during secretion there was a marked vasodilatation in the gas gland, whereas after
vagotomy, and especially after atropine treatment, the;e was considerable vasoconstriction in the gland. But Fange rightly raised the still unresolved question of whcther the vasodilatation occurring during activity
is a primary effect caused by specifically vasodilator nerves or a secondary effect caused by the release of metabolites from cholinergically
activated secretory cells.
B. Spinal Autonomic Nerves
The sympathetic nervous system of selachians consists of a series of
paravertebral ganglia, one or more occurring per spinal nerve, linked
together at most by a loose plexus of nerve bundles. T1,ere is no compact sympathetic chain. The ganglia are connected to the spinal nerves
by white rami communicantes. Young (1933~) claims that gray rami are
absent, i.e., that there is no entry of postganglionic fibers into the spinal
nerves to reach dermal structures, but there is some evidence for sympathetic nervous control of dermal melanophores. The ganglia extend
no further caudally than the posterior end of the mesonephros in adults.
There are no cranial sympathetic ganglia nor is there any semblance of
a sympathetic chain entering the head region; however, this does not
preclude a sympathetic innervation of cranial structures via perivascular
nerve plexuses. There are no prevcrtebral ganglia, and fibers from the
paravertebral ganglia are collected into anterior, middle, and posterior
splanchnic nerves extending to the alimentary canal via plexuses on
the arterial supply. Other fibers run directly to the genital and urinary
ducts.
In teleosts, the sympathetic system has a well-defined structure resembling that found in tetrapods. Paravertebral sympathetic ganglia,
usually two per spinal segment, are linked together regularly to form
two sympathetic chains which fuse to a greater or lesser extent in differ-