The distribution of cholinergic excitatory neurones in the canine gastric wall was studied by recording electrical and mechanical responses to electrical stimulation of the nerves of Latarjet and close intraarterial perfusions of drugs which stimulate nerve and muscle. Electrical stimulation of the anterior nerve of Latarjet produced contractile activity on the anterior side, followed rapidly by activity on the posterior side and vice versa, indicating that the axons of the neurones from each side crossed over to the other. This was not due to the propagation or conduction of electrical response activity, because electrical response activity and contractions induced locally by acetylcholine given into a small artery supplying a segment of stomach did not propagate. The cross-over innervation and the direct innervation were both segmental, in that the response to nerve stimulation dropped out in segments as the branches of the nerves of Latarjet were cut successively. Mainly, preganglionic axons crossed over from the anterior side to the posterior side, but both pre- and postganglionic axons crossed over from the posterior side. This was demonstrated by observing the spread of electrical and mechanical responses, or lack of it, in response to local injections of acetylcholine and dimethylpeprazinium. The study shows that there is a segmental distribution of excitatory neurones in the gastric wall which is appropriate to produce a ring of contraction to control gastric emptying and mixing.