Anatomical view of common carotid artery-external jugular vein area. A. The rabbit was placed in the supine position, a midline neck incision was made and structures in the left neck were exposed. a. Common carotid artery; b. Anterior facial vein; c. Posterior facial vein; d. External jugular vein. B. In the preliminary experiment, a significant boundary between the arterial blood and venous blood was observed after end-to-side anastomosis between the CCA and EJV. C. Before the anterior facial vein and the posterior facial vein join to form the external jugular vein, there is a significant fibrous boundary. D. Longitudinal incision of the veins shows that there is one valve in the junction of the anterior facial vein and the external jugular vein and one valve in the junction of the posterior facial vein and the external jugular vein. Both valves are pointing cephalically to prevent the reflux of venous blood from the chest and abdomen into the head. Without these valves, the venous blood reflux into the head may cause obstruction of the venous drainage from the head and further induce intracranial ischemia and hypoxia (similar to the situation of hanging upside down).