noun
: a small mass of tissue made up of Purkinje fibers, ganglion cells, and nerve fibers, embedded in the musculature of the right auricle of higher vertebrates, representing the remains of the sinus venosus of lower forms, serving as a pacemaker to the heart, and transmitting the impulse to beat by way of the Purkinje's network to the auricles, the atrioventricular node and bundles, and the ventricles — called also sinus node