ABSTRACT
The cardiac automatism, as a physiologic process represents the independence of the cardiac muscle from the organic control. This is its main feature (Gannong 1968). The cardiconducting system is responsible for it (Gannong 1968), which is connected to the sympa thetic system through the cardiac nerves from the cervical ganglia (Truex and Carpenter 1965). Al this, is described by human anatomy (Testut 1954, Gardner 1960, Caso 1965, Truex and Carpenter 1965, Paturet, Rouviere and Delmas 1974) and by mammals anatomy (Davies et al 1952, Grassé 1972), but there is no description of similar structures in low vertebrates. Through a microscopical study of the atrial structure of the heart of 25 specimen of Bufo arunco, we found an intrinsoc ganglion in the septum atrial, which compared to that of a rabbit presented identical structures (Mitchell 1956). Samples of ganglia tissue of Vufo arunco, processed by Bodian's stain (Matoja 1970) show a clear nervous structure, and it is possible, in situ, relate it to the fibers of the cardiac nerve. The morphological and hystological identity between the rabbit and bufo arunco ganglia, permits to think of a functional identy too, that would be the regulation of the caridac contraction through sympathetic system (Paturet 1968). This identity makes us conclude the existence of an intrinsic sumpathetic ganglion in the heart of Bufo arunco