[Topographic and histological study of the sinoatrial node in the Jaffarabadi buffalo (Babalus bubalis Linnaeus, 1758)].

A topographic and histologic study of the sinuatrial node was made in the hearts of 12 buffalo of the Jaffarabadi breed, 8 adults (5 females and 3 males) and 4 term fetuses (3 female and 1 male). The nodal tissue was localized at the junction of the vena cava superior with the right atrium, occupying, more precisely, the entire extent of the terminal groove, the dihedral cavoatrial angle and the first part of the auricular surface of the junction, which is contiguous with this angle. This structure contains cells with single or double nuclei, round or oval in shape, surrounded by a light halo, with scattered chromatin and a well-defined nucleolus, acidophilic cytoplasm containing, in comparison with the common myocardium, few sinuous myofibrils with transverse striations and a larger amount of glycogen. We also observed arteries of small and medium caliber, with veins and nerves accompanying the nodal mass, while the nerve ganglia were situated opposite the sinuatrial node.