The sinuatrial node and its adjacent autonomous ganglia cells in aquatic mammals (A morphological approach)

In a comparative investigation of the sinuatrial node and its vicinity in aquatic mammals and in non professional mammalian divers the great difference in the number of autonomous ganglia cells in the vicinity of the sinuatrial node was described. The computing of the results led to the conclusion, that this morphological approach of the sinuatrial node and its vicinity supports the physiological statement: The deep bradycardia during diving in aquatic mammals is caused by an overruling of the sinuatrial node activity through the influence of the parasympathetic part of the autonomous nervous system. The sinuatrial node and its environs taken from the heart of two dolphins (Lagenorhynchus albirostris, Gray, 1846); four harbour porpoises (Phocoena phocoena, Linnaeus, 1758); four seals (Pusa sibirica, Gmelin, 1788) and three muskrats (Ondatra zibethicus, Linnaeus, 1766). (DBO)