|Calotes (Lizard)||Columba (Pigeon)||Oryctolagus (Rabbit)|
|1. Heart is situated mid ventrally in the anterior part of the body cavity in the pleuro peritoneal cavity behind the sternum.||1. Same way the heart is located.||1. Heart is situated in the thoracic cavity, between the lungs of two sides (Mediastinum). It is present slightly towards the left side.|
|2. Heart is comparatively smaller in size.||2. Heart is comparatively larger in size.||2. Heart is comparatively larger in size.|
|3. It is enclosed by double walled pericardium.||3. It is also enclosed in the double walled pericardium.||3. Same.|
|4. Heart includes a dorsal sinusvenusus aright auricle, a left auricle and a single incom-pletely divided ventricle.||4. Heart is four chambered, sinus venosus is absent in the adult. Completed divided two auricles and two ventricles by inter auricular septum and inter ventricular septum respectively.||4. Same as in columba.|
|5. The three vena cavae or two precavals and a post caval vein open into the sinus venosus.||5. The three vena cavae or two precavals and a post caval empty the blood directly into the right auricle.||5. Same as in pigeon.|
|6. The left auricle receives two pulmonary veins from the lungs.||6. The left auricle receives four pulmonary veins from the lungs.||6. Left auricle receives two pulmonary veins from the lungs.|
|7. The right auricle possess sinu auricular aperture guarded by valve.||7. Absent.||7. Absent.|
|8. The two auricles are completely separated by inter auricular septum. But the inter ventricular septum in the ventricle is incomplete. Hence oxygenated and deoxygenated types of blood is mixed to some extent in the ventricle.||8. Complete inter auricular and inter ventricular septa are present. There is no possibility of mixing the oxygenated blood with deoxygenated blood.||8. Same as in pigeon.|
|9. The heart of lizard is in a transitional stage approcarhing the double circuit stage But it has not reached it completely due to incomplete division of the encircle.||9. The heart is a double circuit heart because of complete division of ventricle into right and left chambers.||9. Same as in pigeon.|
|10. The auriculo ventricular aperture is guarded by two flap like semilumar valves.||10. The right auriculo ventricular aperture is guarded by two large muscular flap like valve and the left by three valves.||10. The right auriculo-uentricular aperture is guarded by tricuspid valve and the left by bicuspid valve (mytral valve).|
11. There are three aortic arches arising from the ventricle.
11. Only two aortic arches originate from the ventricles.
i.e. Right aortic arch is characteristic of birds.
11. Only two aortic arches arise from the ventricles.
|12. Ductus caroticus is present (connection between carotid & systemic arches)||12. Absent||12. Absent|
|13. Lizard's heart presents a transitional heart, since it approaches the double circuit heart but has not yet completely attained. So the heart is less efficient.||13. Avian heart has at tained maximum com olexity and is a double circuit heart, i.e. venous blood is com pletely separated frorr oxygenated blood.||13. Same as in Pigeon.|
|14. Absent.||14. Sinu-Auricular Node and Auriculo ventricular node are present.||14. SA - node and A.V. node are present. In addition bundle of His muscles are also develop.|