Tetrapod probably had a three-chambered heart, as do modern amphibians and reptiles, in which oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enters by separate atria, and is directed via a spiral valve to the appropriate vessel — aorta for oxygenated blood and pulmonary vein for deoxygenated blood. The spiral valve is essential to keeping the mixing of the two types of blood to a minimum, enabling the animal to have higher metabolic rates, and be more active than otherwise. The difference in density between air and water causes smells (certain chemical compounds detectable by chemoreceptors) to
Jugular vein resolution, or coup-de-grace. An alternate explanation for the phrase suggests "to go for the jugular" merely means to attack without restraint. The jugular vein system is essential but not particularly weak or vulnerable, because this venous system is generally found fairly deep in the body. Jugular vein The jugular veins are veins that take deoxygenated blood from the head back to the heart via the superior vena cava. There are two sets of jugular veins: external and internal. The left and right external jugular veins drain into the subclavian veins. The internal jugular veins join with the subclavian veins more