A section through the atrioventricular (AV) region of the heart.
Observe:
1. The neural arch in the C-5–C-6 interganglion region.
2. The junctions of the pre- and postcardinal veins and of the right common cardinal vein with the right sinus horn.
3. The right and left venous valves between the right sinus horn and right atrium.
4. The fusion of the endocardial cushions with the ostium primum above and the interventricular foramen below.
5. The union of the medial and lateral nasal elevations.
Keywords: C-5 / C-6 interganglion region, C-6 ventral primary ramus, axial artery, cerebral vesicle, dorsal atrioventricular endocardial cushion, ependymal zone, esophageal condensation, frontonasal area, fusion point, interventricular foramen, junction of lateral and medial nasal prominences, junction of left precardinal and postcardinal veins, junction of right precardinal and postcardinal veins, lateral atrioventricular endocardial cushion, lateral ventricle, left atrioventricular canal, left atrium, left dorsal aorta, left ventricle, marginal vein, myotome, neural arch, ostium primum, pleural cavity, pleuropericardial opening, right and left valves of sinus venosus, right atrioventricular canal, right atrium, right common cardinal vein, right horn of sinus venosus, right ventricle, septum primum, septum secundum, telencephalon medium, tracheal condensation, transverse sinus, vagus nerve (CN X), ventral atrioventricular endocardial cushion
Source: Atlas of Human Embryos.