THE ANATOMY OF THE HORSE. 23 



In tracing the blood througfh the heart, commencing at the 

 right auricle, we find the two large veins of the body, called the 

 anterior and posterior vena cavas, which empty the impure blood 

 of the body into the right auricle of the heart. It is there guarded 

 by two small valves at the mouth of each vein, while the right 

 auricle contracts, forcing the blood down through the hole in the 

 septum into the right ventricle. It is there guarded by a valve to 

 keep the blood from flowing back, while the right ventricle 

 contracts and forces the blood up into the pulmonary artery, which 

 passes only two or three inches above the heart and divides into 

 two branches, one to the right lung and the other to the left lung. 

 These again divide into other small arteries, which f\ow into what 

 is known, as the capill'Ary network. 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 so as not to allow the 

 blood to flow back while the left auricle contracts to force the 

 blood down through the opening mentioned before into the lefi 

 auricle. This opening is also guarded by valves so as not to allow 

 the blood to flow back while the left ventricle contracts, with great 

 force, to drive the blood up into the common aorta, the largest 

 artery in the body, which passes above the heart two or three 

 inches, and, just below the backbone, 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 under the spine 'just a 

 few inches, where it breaks into other branches, some going to 

 supply the shoulder and front leg; the other branches being two 

 large ones, one passing on each side of the neck under the jugular 

 vein, which 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. In considering 



