A Study of the Enteric Plexuses in Some Amphibians
Authors: Gunn Margaret 
Published: April 2021

The extrinsic nerve-supply to the gut in the frog (Rana temporaria) is contained in the vagus and splanchnic nerves—both of which appear to contain parasympathetic and sympathetic fibres. The vagus supplies the gut from the proximal part of the oesophagus to the most proximal part of the intestine. The splanchnic nerves supply the gut from the oesophagus to the rectum. No vagal fibres accompany the splanchnic nerves. A possible explanation is given for the variable effects produced on stimulation of the extrinsic nerves supplying the gut. A plexus of nerve-fibres is present in the submucosa which probably corresponds to Meissner’s plexus of mammals, but no nerve-cells are present. In the myenteric plexus the nerve-cells are commonly grouped into ganglia in the oesophagus and stomach, but in the intestine the nerve-cells are fairly evenly distributed, distinct ganglia not being present. Cells of three types have been found corresponding to Dogiel’s three types. Type I cells are of two varieties: (a) large, strongly argyrophil cells which are multipolar possessing numerous short dendrites and a very prominent axon; (h) smaller cells having a prominent axon and often unipolar. Type I cells are enclosed in capsules. Type II cells are small multipolar cells with long dendrites. Type III cells are small multipolar cells with shorter dendrites and an axon bearing no collaterals. Cells in the oesophagus and stomach are entirely of Type I. In the intestine these cells are present in fairly large numbers at the most proximal end, but throughout the rest of the intestine they only occur commonly close to the attachment of the mesentery, where they are found singly and fairly eveftly spaced. Cells of Types II and III occur only in the myenteric plexus of the intestine, where they are distributed fairly evenly, not forming distinct ganglia. It is suggested that the Type II and III cells formed the original autonomic nerve plexus of the gut, the Type II cells being motor and the Type III sensory. The Type I cells are the post-ganglionic cells of the parasympathetic system and are an additional motor contribution to the plexus. The endings of the pre-ganglionic parasympathetic fibres on the ganglion cells may take any of three forms : (a) pericellular varicose endings which occur on the large variety of Type I cell ; (b) pericapsular varicose endings which are borne by the smaller variety of Type I cell ; and(c) club-shaped endings occurring on the larger Type I cells. The type of synapse formed by the processes of cells of Types II and III consists of the simple endings of their processes on the cell bodies or dendrites of other cells, or the passing contact of their processes with the bodies of other cells. Fine varicose fibrils have been observed on the surface of muscle-cells. These are presumably the distal ends of the cell processes and sympathetic fibres which form the motor endings. The types of sensory endings which have been found are: (a) typical sensory varicose endings spread out in the submucosa of the oesophagus and rectum; those in the oesophagus originating from vagal fibres; and (ft) Pacinian corpuscle in the submucosa of the intestine. The ‘interstitial cells of Cajal’ form an apparently anastomosing network in the gut-wall which appears to be distinct from the anastomosing Schwann plasmodium which covers the nerve-fibres.