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It was shown in acute and chronic degeneration studies that the nerve elements of the cat small intestine belong to two according to whether they are extrinsic or intrinsic in origin. Part of the extrinsic nerve fibres originate from the vagus nerve and can be found on both intestinal plexuses, the other fibres are processes of the coeliac ganglion and occur in the first place in the vascular tunica adventitia. The intrinsic nerve cells may be classified into three groups on grounds their ultrastructure the number of synapses and processes on their surface. The synaptic connections between the different nerve cells of the internal plexuses were confirmed on chronic isolated of intestinal loops. The local reflexes provided by these connections are held responsible for peristalsis, the functional modifications of the mucosal pattern and the movements of the villi.