Changes

Within the cardiogenic plate, angiogenic cell clusters give rise to a horseshoe-shaped structure known as  the endocardial tube. The lateral limbs of the horseshoe-shaped construction form the left and right endocardial tubes. The mesodermal cells anterior to this form the septum trnsversum. The embryonic disc undergoes a process of folding and the endocarcial tubes and septum tranversum are rotated 180 degrees. The endocardial tubes are brought together and fuse to form the cardiac tube. The wall of the tube differentiates into the endocardium and the myocardium. The myocardium secretes an extracellular matrix known as caridac jelly, this causes areas of the tube to distend forming distinct regions, the Bulbus cordis, the Primitive ventricle, the Atrioventricular sulcus, the Primitive atria and the Sinus venosus.

Within the cardiogenic plate, angiogenic cell clusters give rise to a horseshoe-shaped structure known as  the endocardial tube. The lateral limbs of the horseshoe-shaped construction form the left and right endocardial tubes. The mesodermal cells anterior to this form the septum trnsversum. The embryonic disc undergoes a process of folding and the endocarcial tubes and septum tranversum are rotated 180 degrees. The endocardial tubes are brought together and fuse to form the cardiac tube. The wall of the tube differentiates into the endocardium and the myocardium. The myocardium secretes an extracellular matrix known as caridac jelly, this causes areas of the tube to distend forming distinct regions, the Bulbus cordis, the Primitive ventricle, the Atrioventricular sulcus, the Primitive atria and the Sinus venosus.

At this point blood enters the caridac tube at the posterior end. The bulbis cordis loops to the right and splits into two new bulges, the conotruncus and the right ventricle. This causes the primitive atrium to be displaced dorsally. The ventricles expand while the conotruncus dives into to further bulges, the truncus areteriosus (anterior) and the conus cordis (posterior). The atria expand dorsally and also on either side of the truncus arteriosis, this gives rise to the formation of two chambers, the left and right atria. The sinus venosus is located  on the dorsal aspect of the interconnected atria. The sinus venosus is composed of a left and right horn, the majority of the left horn is lost, meaning that the communication between the sinus venosus and the atria, the sinoatrial opening, is displaced to the right atria. This then means the left side of the atrium is devoid of blood vessels . The developing heart combats this by sprouting blood vessles that connect the left atrium to the lungs. The sprout splits into four channels, providing two vessels per lung.

At this point blood enters the caridac tube at the posterior end. The bulbis cordis loops to the right and splits into two new bulges, the conotruncus and the right ventricle. This causes the primitive atrium to be displaced dorsally. The ventricles expand while the conotruncus divides into two further bulges, the truncus areteriosus (anterior) and the conus cordis (posterior). The atria expand dorsally and also on either side of the truncus arteriosis, this gives rise to the formation of two chambers, the left and right atria. The sinus venosus is located  on the dorsal aspect of the interconnected atria. The sinus venosus is composed of a left and right horn, the majority of the left horn is lost, meaning that the communication between the sinus venosus and the atria, the sinoatrial opening, is confined to the right atria. This means the left side is devoid of blood vessels . The developing heart combats this by sprouting blood vessles that connect the left atrium to the lungs. The sprout splits into four channels, providing two vessels per lung.

===Atrial Septation===

===Atrial Septation===