Bird This pericardial sac is filled with a serous fluid for lubrication. The heart itself is divided into a right and left half, each with an atrium and ventricle. The atrium and ventricles of each side are separated by atrioventricular valves which prevent back flow from one chamber to the next during contraction. Being myogenic, the heart's pace is maintained by pacemaker cells found in the sinoatrial node, located on the right atrium. The sinoatrial node uses calcium to cause a depolarising signal transduction pathway from the atrium through right and left atrioventricular bundle which communicates contraction to the ventricles. The
Lunar node about 0.94901 Gregorian year, as do descending-node eclipses. The nodes are called by different names in different areas of the world. In ancient European texts, the ascending node is referred to as the dragon's head ("Caput Draconis", or "Anabibazon"). Its symbol is , the astronomical and astrological symbol for the dragon's head. By the same analogy, the descending node is also known as the dragon's tail ("Cauda Draconis", or "Catabibazon"), and its symbol is the inversion of that of the ascending node: . In Hindu astronomy, the ascending node ☊ is called "Rahu" and the descending node ☋ is called