On the plasticity of form and structure of enteric ganglia.

The nervous tissue within the wall of the alimentary canal consists of intramural nerves and intramural neurons and constitutes the enteric nervous system. This is indeed a system in the sense that its elements are interconnected, well integrated, and serving modulated physiological roles. The traffic of nerve signals proceeds in all directions, namely orally and aborally, circumferentially, across the thickness of the wall, and from and to extrinsic ganglia. There is, it seems, very little hierarchical organization among the neurons of this system. Morphologically, the system is remarkable for its extent and for its structural compactness; in contrast, it is relatively well accessible to experimental procedures, including surgery. The enteric nervous system extends from the oesophagus to the anal canal, inclusive, and it is therefore almost as long as the trunk. In effect, this neural network is several times longer than the length of the body, on account of the long course of the small and large intestines. Connected to the central nervous system by efferent parasympathetic cranial fibres through the vagus nerve and parasympathetic sacral fibres, to prevertebral ganglia of the solar plexus and paravisceral ganglia of the pelvic plexus by post-ganglionic fibres, and to dorsal root ganglia providing afferent fibres, the enteric nervous system can nevertheless per-