INTERNAL STRUCTURE -

• Wall of auricles are thin than wall of ventricles, because they have to push the blood to ventricles only situated close to them.
• Walls of ventricles are thick as they have to pump the blood quite far away. Wall of left ventricle is 3 times thicker as it has to pump the blood to complete body.
• In wall of ventricle tendinous cords present.
• Inner wall of ventricle is raised into low muscular ridges as columnae carneae and few large muscular elavation as papillary muscles.
• Between ventricles inter ventricular septum present, bent to right side.
• Lumen of left ventricle is large and lumen of R.V. is small and semilunar shape.
• Between auricles and ventricles A.V. node present, from it bundle of His orginate, gives its branches as purkinje fibres in wall of ventricles.
• Between 2 auricles inter auricular septum present. In emrbyo in it foramen ovalis aperture present, that converts in to a fossae ovalis on birth time.
• In R. A. 2 opening present of pre caval & post caval. (In rabbit 3 openings).
• On opening of pre cavals eustachian valve present.
• Behind it coronary sinus opens on it Thebasius valve present.
• In L.A. pul. veins open by common aperture (without valve).
• In R.A. S.A. node or pace maker or heart of heart or node of Keith & Flack present.
• It is made up of cardiac muscles & stimulate heart beat.
• It is connected to vagus nerve. Pace maker system consists of pulse generator & electrodes.
• Both auricles open into ventricles by auriculo ventricular valve.
• In right side it is made up of 3 flaps i.e. tricuspid valve, lower edges of valve are fixed to papillary muscles of ventricle wall by chordae tendinae fibres.
• In left side it is bicuspid or Mitral valve. Both valves are one way i.e. allow blood from A to V not vice versa.
• From R.A. pul. aorta is originated from L.A. carotico systemic arch is originated.
• At the point of origin in both 3-3 similunar valves present, that do not allow blood to come back to ventricles.
• In embryo at their crossing a duct ductus arteriosus present also known as duct of Botelli, which later on convert into ligament arteriosum.