Species range in size from the hefty Common Raven (Corvus corax), at 1.5 kg (3 lb 5 oz) and 70 cm (2 ft 3 in), to the diminutive Short-tailed Pygmy Tyrant (Myiornis ecaudatus), at just 4.2 g (0.14 oz) and 6.5 cm (2 Â½ in).
The heart receives its own supply of blood from the coronary arteries. Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet. These arteries and their branches supply all parts of the heart muscle with blood.hen the coronary arteries narrow to the point that blood flow to the heart muscle is limited (coronary artery disease), collateral vessels may enlarge and become active.
The largest artery from the heart is called the aorta. This artery branches into smaller and smaller vessels before finally reaching the tiny capillaries where oxygen and nutrients are delivered to organs and tissues. The other main artery from the heart goes to the lungs where its blood picks up oxygen.Veins are the blood vessels that carry blood back to the heart. They have much thinner walls than arteries and are under less pressure.he other main artery from the heart goes to the lungs where its blood picks up oxygen. Veins are the blood vessels that carry blood back to the heart. They have much thinner walls than arteries and are under less pressure.