抄録
1. A structure (muscle fascicle) resembling a false-tendon was occasionally found (in 12 of 23 animals) in the right atrium of the monkey, Macaca irus, at a geographical location corespond, ing to the usual site of the specialized conduction system of the atrium, a subject that has long been studied by this author. This structure generated action potentials preceded by a slow diastolic depolarizations. The cells constituting this structure differed, both optic-microscopically and electron microscopically, from ordinary atrium muscle cells in that the cells were small in size, irregular in arrangement and with in nuclei, a histological feature that makes this structure appear more or less like nodal tissues. 2. Investigation of serial sections made to-wards too directions, that is, upward to the sinus node and downward to the A-V node from this structure, showed that this structure was in continuity with muscle bundles of similar nature towards both directions. 3. Investigation on the hearts of 62 rabbits by means of microelectrodes showed that, when a shift of pacemaker from the heed to the tail of the sinus node has been previously produced by the application of acetylcholine to the sinus node, section of the systema septoangularis post. resulted in a complete dissociation between sinus node and A-V node. 4. The location of the tip of microelectrode was verified my effecting electrophoretic migration of cobalt hydrochloride solution, both for the head of the sinus node (usual site of the pacemaker) and for the tail of the sinus node (site of a pacemaker after the application of acetylcholine).
