50 THE VETERINARY SCIENCE 



This network is situated around the air cells of the lungs, 

 where, by a process, the blood gives off carbonic acid gas, 

 which is breathed out along with the air. The blood takes in 

 the oxygen from the pure air, which changes the color of the 

 blood from a black red to a bright red. This is a point of 

 importance to note as it shows that stables should be well 

 ventilated so that animals can have plenty of pure air. The 

 blood now flows into the pulmonary veins, which carry the 

 pure blood back to the heart to be emptied into the left 

 auricle. Here these veins are guarded with valves to prevent 

 the blood from flowing back while the left auricle contracts 

 to force the blood down through the opening mentioned 

 before into the left ventricle. This opening is also guarded 

 by valves to prevent it from flowing back while the left 

 ventricle contracts, with great force, to drive the blood up 

 into the common aorta, the largest artery in the body. This 

 artery passes above the heart two or three inches, and, just 

 below the backbone. It breaks into branches, one passing 

 forward and supplying the parts of the body in front of the 

 heart, the other branch passing backward under the spinal 

 bones, supplying the parts of the body behind the heart. 



The branch which goes forward runs just a few inches 

 under the spine where it breaks into other branches, some 

 going to supply the shoulder and front leg; the other 

 branches being two large ones, pass on each "side of the 

 neck under the jugular vein. They are called carotid arteries. 

 These give off small branches, as they pass up the side of 

 the neck, to feed the muscles and other parts thereof, while 

 just below the butt of the ear, this artery breaks into three 

 large branches, which go to supply the brain and different 

 parts of the head. The branch which runs backward from 

 the heart is a very long, large artery, passing just below the 

 spine, between the kidneys, breaking up about six inches 

 behind them into four large branches — two on the left and 

 two on the right side. That on the left goes to supply the 

 left hip and organs in the pelvic or hip cavity, while the 

 other passes down the left leg to supply it with blood ; that 

 on the right side helps to supply the right hip and pelvic 

 cavity, while the other passes down the right leg. This large 

 branch, in passing back along the spine, gives off small 

 branches — one to the liver, one to the spleen, one to the 

 stomach, branches to the large and small bowels, and one to 

 each kidney. 



