114
GRAEME CAMPBEI L
lampreys is innervated from the spinal cord. Support for a vasomotor
function of the sympathetic has come from the observation of Leont’eva
(1966), who showed histochemically that there is an adrenergic innervation of blood vessels in cyclostomes.
Both lampreys and hagfish possess a rich subcutaneous nerve plexus
containing uni- and bipolar nerve cells, a feature unique among the
vertebrates. The ganglion cells are innervated by spinal nerve fibers and
arc almost certainly autonomic (see Bone, 1963). A number of functions
could be subserved by the fibers. Bone (1963) has found that the
plexus is particularly concentratcd at the orificrs of the slime glands in
Myxine, associated with bundles of smooth muscle which form sphincters
for thc glands. In addition, the plexus is continuous about the walls of
the gland and may regulate the activity of smooth muscle cells around
the gland. Bone has also noted that cell bodies in the plexus often lie
beside the small blood vessels of the subcutis, and he has suggested
that the plexus may control blood flow in the subcutaneous blood sinuses.
One further function may be proposed for the subcutaneous plexus,
that of chromatophore control. Color changes in most cyclostomes appear
to be extremely slow if they occur at all (see Young, 1935). However,
Wild (1903) has reported that Petromyzon marinus shows dramatic and
rapid color changes, indicating a nervous control of the chromatophores
in this species, presumably via the plexus.
111. GNATHOSTOMATOUS FISH
Physiological observations on the autonomic nervous system of
gnathostonie fishes have been virtually restricted to selachians and
teleosts. Although there are conspicuous anatomical differences between
the autonomic systems of these two groups, especially in the arrangement of the spinal outflow, it seems likely that there are no gross physiological differences.
A. Cranial Autonomic Nerves
Autonomic fibers leave the brainstem of selachians in the oculomotor,
facial, glossopharyngeal, and vagus nerves. In telvosts, the outflow is
restricted to the oculomotor and vagus ncwc1s. There have been no
physiological investigations of the autonomic functions mediated by the
selachian VIIth and INth nerves, but it has been suggested that both
outflows providc vasomotor fibcrs to the pharyngeal region. Prcwmably
this function has bccn taken over completely by the wgus in teleosts.
GRAEME CAMPBEI L
lampreys is innervated from the spinal cord. Support for a vasomotor
function of the sympathetic has come from the observation of Leont’eva
(1966), who showed histochemically that there is an adrenergic innervation of blood vessels in cyclostomes.
Both lampreys and hagfish possess a rich subcutaneous nerve plexus
containing uni- and bipolar nerve cells, a feature unique among the
vertebrates. The ganglion cells are innervated by spinal nerve fibers and
arc almost certainly autonomic (see Bone, 1963). A number of functions
could be subserved by the fibers. Bone (1963) has found that the
plexus is particularly concentratcd at the orificrs of the slime glands in
Myxine, associated with bundles of smooth muscle which form sphincters
for thc glands. In addition, the plexus is continuous about the walls of
the gland and may regulate the activity of smooth muscle cells around
the gland. Bone has also noted that cell bodies in the plexus often lie
beside the small blood vessels of the subcutis, and he has suggested
that the plexus may control blood flow in the subcutaneous blood sinuses.
One further function may be proposed for the subcutaneous plexus,
that of chromatophore control. Color changes in most cyclostomes appear
to be extremely slow if they occur at all (see Young, 1935). However,
Wild (1903) has reported that Petromyzon marinus shows dramatic and
rapid color changes, indicating a nervous control of the chromatophores
in this species, presumably via the plexus.
111. GNATHOSTOMATOUS FISH
Physiological observations on the autonomic nervous system of
gnathostonie fishes have been virtually restricted to selachians and
teleosts. Although there are conspicuous anatomical differences between
the autonomic systems of these two groups, especially in the arrangement of the spinal outflow, it seems likely that there are no gross physiological differences.
A. Cranial Autonomic Nerves
Autonomic fibers leave the brainstem of selachians in the oculomotor,
facial, glossopharyngeal, and vagus nerves. In telvosts, the outflow is
restricted to the oculomotor and vagus ncwc1s. There have been no
physiological investigations of the autonomic functions mediated by the
selachian VIIth and INth nerves, but it has been suggested that both
outflows providc vasomotor fibcrs to the pharyngeal region. Prcwmably
this function has bccn taken over completely by the wgus in teleosts.