The Autonomic Nervous System of Selachians

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Abstract
1. The rami cornmunicantes of Selachians contain only preganglionic fibres; there are no recurrent grey rami and therefore no sympathetic nerves to the skin, chromatophores, or somatic muscles. This probably accounts for the absence of the sympathetic from the head and tail regions. 2. In accordance with (1) it was found that cutting of the spinal nerves produced no local colour changes in the skin, neither was adrenaline found to have any action on the chromatophores. 3. There are no long pre- or post-ganglionic pathways in the sympathetic and therefore no true sympathetic chains, though the ganglia of adjoining segments are sometimes connected. The arrangement is thus more nearly segmental than that of Teleosts or Tetrapods. 4. No sympathetic ganglia were found in the tail of adult Scyllium or Torpedo, but in embryos of these forms scattered motor neurones were found in connexion with the caudal blood-vessels. 5. Stimulation of the vagus caused movements of the cardiac stomach, of the anterior splanchnic nerves movements of the pylorus and pyloric stomach. Stimulation of the middle and posterior splanchnic nerves caused movements of the intestine, colon, and rectum. Pinching the intestine evoked a characteristic progressive reflex contraction, ending in the extrusion of faeces. 6. The posterior suprarenal bodies differ in the two sexes, those of the male being much the larger, although the number of cells giving the chrome reaction is the same in both. 7. The suprarenal tissue is very plentifully supplied with post-ganglionic fibres, which could be seen actually in connexion with their cell-bodies. The hypothesis of Elliott that the chromophil cells themselves represent post-ganglionics is therefore disproved in this case. 8. The structure of the autonomic neurones is described in detail, especially the methods by which contacts are made between them. 9. No motor cells were found in the vagus ganglion of embryo or adult Scyllium, but they do occur on the post-trematic rami of all the branchial nerves. 10. A small profundus nerve was found to be present in Scyllium, though not in all individuals. 11. There is little evidence for the existence in fish of functionally antagonistic sympathetic and parasympathetic systems, and it is suggested that these systems in Tetrapods represent specializations within a single segmental set of visceral motor fibres, running primarily through the dorsal roots but coming to pass through the ventral roots in those segments in which the roots join.