JUDGING DAIRY CATTLE 79 



lacteals that are contained in the villi mentioned and these 

 join a long tube that runs beneath the spine and finalh- 

 reaches the thoracic duct, which also receives all the fluid 

 coming from the other lymphatics in the cow. The thoracic 

 duct empties its contents about the region of the first rib into 

 a great vein (the anterior vena cava) wliich opens into the 

 right side of the heart, so all the digestible constituents of 

 the food are now in the blood and have reached the right 

 side of the heart. From here the blood goes to the lungs to 

 be purified by the air that is breathed in and then it again 

 goes back to the left side of the heart to be pumped through 

 the arteries to the various portions of the body. Several 

 branches run to the various organs of the body but that 

 which goes to the mammary gland is of chief interest in 

 the function of making milk. The aorta runs along under 

 the spinal column and finally reaches the femoral arterj^ 

 which is about parallel with the femur or thigh bone. This 

 throws off" a branch (prepubic; which again branches into 

 another (the external pubic) and this again after it passes 

 through the inguinal ring divides into two branches (the 

 anterior or subcutaneous artery, and the posterior abdominal 

 or mammary artery) and from these the mammary gland 

 receives its supply, as they branch into all the regions of the 

 udder. 



Following the blood still further, it passes through the 

 udder and appears outside of it in what are known as the 

 milk veins. They run along the belly, pass into the body, 

 and finally direct the blood to the heart again. In respect 

 to the function and relations of the organs up to this point, 

 we can understand that the stomach and its accessories per- 

 form the greatest amount of work in making food into blood, 

 while the lungs purify it, aiid the heart propels it to those 

 parts that are in most need of it. 



131. Function of the Udder. In the dairy cow the udder 

 is an important organ, for it directly performs the work of 



