1. Secretory nerve fibres to the parotid gland of the dog have been found in the adventitia of the internal maxillary artery. In dogs under chloralose anaesthesia the course of these fibres from the mandibular nerve to the gland was determined by electrical stimulation at different sites. Secretion induced by these nerves was abolished by atropine but not by hexamethonium.2. In dogs in light barbiturate anaesthesia parotid secretion was evoked reflexly by pouring citric acid on the tongues. After division of the auriculo-temporal nerve and the nerves on the artery this secretion disappeared in about half the experiments and was greatly reduced in the others.3. The maximal secretory rate which could be obtained reflexly from the normally innervated parotid gland was first estimated in light barbiturate anaesthesia. Chloralose was then given and the auriculo-temporal nerve and the nerves on the artery were electrically stimulated together; in about half the experiments this could produce secretion at a rate as high as that obtained reflexly.4. By separate and simultaneous stimulation of different sets of nerve fibres convergence of the secretory fibres to the glandular cells could be demonstrated.5. It is concluded that a large number of post-ganglionic, cholinergic secretory fibres to the canine parotid gland run on the internal maxillary artery. In some dogs a small number of fibres seem to have escaped detection. Possibly they may reach the gland by way of the facial nerve.
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