Anatomy of the sinus node was studied in six camel hearts (Camelus dromedarius) with serial histologic sectioning. The sinus node in this species of animal was located 0.5 mm beneath the epicardium, near the junction between the cranial vena cava and the right atrium at the sulcus terminalis. Its shape was elongated, bent oblong with 28.25 mm length, 5.75 mm width and 5.38 mm thickness. The maximum section area was 101.66 mm2. The central artery of the node originated from the circumflexus branch of the left coronary artery and, throughout its length in the substance of the sinus node, had an internal elastic membrane. Histologically, the sinus node of this animal contained a central artery and a framework of collagen fibres, which were distributed around the central artery. The nodal cells were irregularly organized around the central artery and two types, i.e. "p' cells and transitional cells were present. The "p' cells had a perinuclear clear zone but the transitional cells contained more myofibrils. The intercalated discs were not present. At the periphery of the sinus node there were many nerve fibres and a ganglion. The purkinje fibres were present within atrial myocardium, as well as within ventricular myocardium. The glycogen content of the sinus nodal cells was higher than that of the atrial myocardial cells.

The detailed coronary arterial anatomy of seven camels was studied and compared with that of horses and cattle. In camels, there is a bilateral coronary supply, the right coronary artery being the larger. The left coronary artery follows the same pattern as that in horses. The ramus collateralis proximalis in camels separates off some distance away from the origin of the ramus interventricularis paraconalis, as in horses, whereas it separates of very quickly in cattle. The ramus collateralis distalis has two branches in camels, whereas the left distal ventriculi ramus does not branch. The ramus angularis is also absent but the left distal atrii ramus is present.

A bs trm t Ghazi, S.R., Tadjalli, M. and Baniabbas, A. 1998. Anatomy of the sinus node of domestic cats (Felis catus). J. Appl. h i m . Res., 14: Anatomy of the sinus node was studied in 10 hmestic cats (5 males and 5 females). In the feline heart, the sinus node lied 0.Q6mm-0.11 mrn beneath the epicardiurn, at terminal sulcus, near the junction between the cranial uena caua and the right atrium, its shape was almost triangglar. Its cranial end was near the myocardium of the atrial wall and it was narrow, while the caudal end was near the myocardium of the right auricle and it was wide. The dimensions of the sinus node in male cats were 2.78 mm x 2.80 mrn x 0.54 mm, and in the female cats 2.75 mm x 2.64 mm x 0.45 mm. Histologically, the sinus node of cats contained nnrmally a dense collagen frame and the cells with perinuclear clear zone (P) and transitional cells (7J were the principal cells of parenchyma. Since these cells contained less myofibrils than working myocardium, thefore> they were distinctively paler. The "Po cells (7-9.75~) were bigger than "T" cells (5-6 p) and smaller than the ordinary myocardial cells (9-71.87 1.1). At the junction between "T" cells and "F" cells intercalated discs were not seen. While the glycogen content of the "P" cells was very little, it was more in "T" cells almost at the same level as ordinary atrial myocardial cells. 57-64.57

The anatomy and histology of the atrioventricular bundle (AVB) was studied in the heart of six camels (Camelus dromedarius). The trunk of the atrioventricular bundle (bundle of His) was a direct continuation of the atrioventricular (AV) node with no sharp line of demarcation between the node and the bundle. The atrioventricular bundle ran through the fibrous trigone and entered the lower part of the interventricular membranous septum, beneath the right endocardium, then lay over or slightly to the side of the centre of the muscular interventricular crest. The AVB of camels measured 4.12 +/- 1.00 mm in length, 3.66 +/- 1.13 mm in width and 1.13 +/- 1.85 mm in thickness, its maximum sectional area being 12.68 +/- 6.13 mm2. Histologically, the AVB in the heart of camels comprised multiple strands of Purkinje cells separated by collagen fibres and surrounded by connective tissue. It resembled that in human beings and dogs except that, in camels, intercalated discs were present at the intercellular connections in the AVB.

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