Internal structure of Heart:
The right auricle is bigger than the left auricle. Both the auricles are thin walled. The right auricle and the left auricle are separated from each other by a verticle septum called interauricular septum. There is large aperture in the dorsal wall of the right auricle. This aperture is known as sinu auricular aperture. The sinu auricular aperture is guarded by a pair of valves. The common pulmonary vein opens in the dorsal wall of the left auricle through a small oblique aperture devoid of any valves. Auriculo-ventricular septum, a horizontal septum, internally separates the two auricles from the ventricle. The right and left auricle open into the ventricle through a single aperture called auriculo ventricular aperture. The auriculo ventricular aperture is guarded by a four flapped valve called auriculo ventricular valve. Several chordae tendinae are attached to the margin of the four flaps of the auriculo ventricular valve. The chordate tendinae are thread like chords which are attached to the muscular wall of the ventricle at their other ends. The truncus arteriousus arises from the anterior and ventral part of the lumen of the ventricle. The truncus anteriosus emerges and runs forward obliquely on the ventral surface of the right auricle. There are three semilunar valves at the proximal end in the truncus arteriosus. The basal, broad and thick walled portion of the truncus arteriosus is known as conus arteriosus.
The anterior, distal, thin walled and narrow portion of the truncus arteriosus is known as venral aorta. There is a longitudinal spinal valve in the lumen of conus arteriosus. The dorsal margin of this valve is attached to the dorsal wall of the conus. The ventral margin of this valve is freely suspended in the lumen. This valves divides the lumen of conus arteriosus into a left cavum pulmocutaneum and right cavum aorticum. The left cavum pulmocutaneum and right cavum aorticum are incompletely separated from each other. There is an aperture of common pulmocutaneous arch in the anterior part of the cavum pulmocutaneum. The aperture is guarded by a valve. The blood entering the cavum pulmocataeum enters and flows through the pulmocutaneous arches due to this type of structure. The ventral aorta divides into two lateral aortae. Each lateral aorta is divided into two arches: a carotid arch and systemic arch.