A Nabipur - Department of Anatomical Sciences School of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad- Iran
S Khanzadi - Department of Anatomical Sciences School of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad- Iran
GH Moradi - Department of Anatomical Sciences School of Veterinary Medicine, Ferdowsi University of Mashhad, Mashhad- Iran

Anatomy of the sinu - atrial node was studied in 5 female goats In the goat's heart, the sinu - atrial node lied 0.18 mm - 0.2S mm beneath the epicardium, at terminal sulcus, near the junction between the cranial vena cava to, lateral wall of th4! right atrium and the right auricle, its shape was elongated and relatively cone shaped. Its cranial end was near the myocardium of the right auricle and caudal endwas near the myocardium of atrial wall. The caudal end was narrower than the cranial end. Average of dimensions of thesinu - atrilal node were 12.75 mm x 1.5 mm x 1.7 mm. Histologically, the sinu - atrial node of goats contained normally a dense collagen frame and the cells with perinuclear clear zone (P) and transitional cells (T) were the principal <:ells of paranchyma. since these cells contained less myofibrils than working myocardium , therefore , they were distinctively paler. The "p" cells were bigger than "T"cells and smaller than the ordinary myocardial cells. At the junction lM~tween "T" cells and "P" cells intercalated discs were not s;een. The sinu - atrial node of goats lacked the central artery, but near the central section and toward the cranial maJrgin there is a distinct arteriole that supplies the node.

Anatomy, Sinu - Atrial Node, Goats, P cells, 'T cells