GRAEME CAMPBELL
11. CYCLOSTOMES
A. Cranial Autonomic Nerves
The oculomotor nerve is absent in hagfish, in which the lateral eyes
are degenerate. The eyes of lampreys are also small, but oculomotor
nerves are found. Anatomical evidence for an autonomic component of
the oculomotor in lampreys is controversial, and there would appear to
be no function for such a component since the eyes are probably completely devoid of intrinsic musculature.
An autonomic component of the facial nerve has been claimed for
Myxine, largely on the basis of brainstem analysis. Lindstrom (1949)
has suggested that the autonomic fibers innervate the lingual artery,
but he does not exclude the possibility that the fibers are afferent. No
physiological investigations of this nerve have been made.
In both hagfish and lampreys, the two vagus nerve trunks unite to
form a cardiac plexus, lying on the gut wall, containing numerous nerve
cell bodies and a few ganglionic aggregations. From this plexus, autonomic fibers are distributed to the region of the heart, major veins, gall
Madder, and, via an unpaired nerve trunk, to the entire length of the intestine (sce Nicol, 1952; Johnels, 1956, 1957; Peters, 1963; Fange et al.,
1963). The intestinal wall contains a nervous plexus with numerous cell
bodies (Brandt, 1922), some of which may be sensory neurons ( Milokhin, 1958, 1959a,b). The neurons become sparse in the posterior region
of the gut (Fange et al., 1963), although the fiber plexus persists. Many
of these enteric neurons are probably innervated by vagal fibers.
Of the vagal innervation systems, that of the heart has been studied in
greatest detail. Greene (1902) first reported that the heart of the hagfish
Polistotrema ( = Bdellostoma) stouti was not affected by stimulation
of the vagus nerve, or indeed of any other nerve. This was confirmed
for the same species by Carlson (1904) and for another hagfish, Myxine
glutinosa, by Augustinsson et al. (1956). In agreement with this obseniation, no nerve fibers were found during an electron microscopic investigation of Myxine heart (Hoffmeister et al., 1961). Normal hearts of both
species are virtually unaffected by acetylcholine and by catecholamines
(Ostlund, 1954; Fange and Ostlund, 1954; Chapman et al., 1963). In
contrast, the lamprey heart is innervated by the vagus nervcs. The main
response to stimulation of the medulla oblongata is an acceleration of
the heart followed by a period of deceleration after periods of intense
stimulation ( Lampetra, Zwaardemaker, 1924; Augustinsson et a)., 1956),
although a period of inhibition preceding the acceleration has been re-
11. CYCLOSTOMES
A. Cranial Autonomic Nerves
The oculomotor nerve is absent in hagfish, in which the lateral eyes
are degenerate. The eyes of lampreys are also small, but oculomotor
nerves are found. Anatomical evidence for an autonomic component of
the oculomotor in lampreys is controversial, and there would appear to
be no function for such a component since the eyes are probably completely devoid of intrinsic musculature.
An autonomic component of the facial nerve has been claimed for
Myxine, largely on the basis of brainstem analysis. Lindstrom (1949)
has suggested that the autonomic fibers innervate the lingual artery,
but he does not exclude the possibility that the fibers are afferent. No
physiological investigations of this nerve have been made.
In both hagfish and lampreys, the two vagus nerve trunks unite to
form a cardiac plexus, lying on the gut wall, containing numerous nerve
cell bodies and a few ganglionic aggregations. From this plexus, autonomic fibers are distributed to the region of the heart, major veins, gall
Madder, and, via an unpaired nerve trunk, to the entire length of the intestine (sce Nicol, 1952; Johnels, 1956, 1957; Peters, 1963; Fange et al.,
1963). The intestinal wall contains a nervous plexus with numerous cell
bodies (Brandt, 1922), some of which may be sensory neurons ( Milokhin, 1958, 1959a,b). The neurons become sparse in the posterior region
of the gut (Fange et al., 1963), although the fiber plexus persists. Many
of these enteric neurons are probably innervated by vagal fibers.
Of the vagal innervation systems, that of the heart has been studied in
greatest detail. Greene (1902) first reported that the heart of the hagfish
Polistotrema ( = Bdellostoma) stouti was not affected by stimulation
of the vagus nerve, or indeed of any other nerve. This was confirmed
for the same species by Carlson (1904) and for another hagfish, Myxine
glutinosa, by Augustinsson et al. (1956). In agreement with this obseniation, no nerve fibers were found during an electron microscopic investigation of Myxine heart (Hoffmeister et al., 1961). Normal hearts of both
species are virtually unaffected by acetylcholine and by catecholamines
(Ostlund, 1954; Fange and Ostlund, 1954; Chapman et al., 1963). In
contrast, the lamprey heart is innervated by the vagus nervcs. The main
response to stimulation of the medulla oblongata is an acceleration of
the heart followed by a period of deceleration after periods of intense
stimulation ( Lampetra, Zwaardemaker, 1924; Augustinsson et a)., 1956),
although a period of inhibition preceding the acceleration has been re-