UNSW Embryology

High pressure pathway from the ventricles into the aortic system.

D7: Apex of left ventricle: spongy network of endocardium; a small dorsal cavity (part of the intraembryonic coelom which will become the pericardial cavity - no pericardium yet); mesenchymal jelly of body wall.

C6: Aperture in interatrial septum, the ostium (foramen) primum. L and R atrioventricular canals. Note the L auricle is not separated from L atrium, the plane of section has caught the wall fold at the region where the auricle connects.

C5: Communication of L auricle with left atrium.

C4: Transition from R ventricle to the outflow tract, including the truncus arteriosus and complete interatrial septum (cf. C5).

C3: Truncus arteriosus. Atria. Right venous valve in R atrium.

C7-C3: Return to C7 and proceed to C3, noting how left ventricular blood has to pass obliquely across right ventricle to exit from heart via the outflow tract and truncus arteriosus.

B5 small "6th" pharyngeal arch artery either side of the laterally-compressed pharynx.

B3: Cranial end of aortic sac. 4th pharyngeal arch arteries and emerging 3rd pharyngeal arch artery. Note dark thyroid primordium ventral to origin of 3rd arch arteries.

 B2: (lst and 2nd pharyngeal arch arteries not seen. 3rd arch arteries. Bilaterally, communication of 4th arch artery (at sides of pharynx) with dorsal aorta.

B1: 3rd arch arteries. Dorsal aortae. (Superior cardinal veins lateral to aortae).

A7: On left side, communication of 3rd arch artery with aorta (i.e. occurring cranial to the 4th arch communication). From here on the arterial blood is distributed through fine branches to vessels outside the brain (pial plexus).

Next- caudal path of the arterial blood