JUDGING THE DAIRY TYPE OF CATTLE 297 



The arteries conduct blood from the heart to the tissues. 

 They arise from a common trunk, the aorta, which divides 

 and subdivides like the branches of a tree. The arteries 

 are very elastic, and contract and expand. The capillaries 

 are extremely fine tubes in the body tissue, terminating in 

 the arteries, which absorb part of the nutrients of the food 

 into the blood. The veins are channels by which the blood 

 returns to the heart. They are arranged like the arteries, 

 but are usually of larger 'capacity. The nutrients of the 

 food are taken up in the process of digestion, mainly in the 

 intestines, the inner coatings of which .are lined with 

 minute . finger-like projections of microscopic size, called 

 villi. In the center of each of these villi is a vessel, the 

 lacteal, which connects with the lymphatic system. Sur- 

 rounding the lacteal is a network of capillaries which con- 

 nect with the blood system. Here, in the villi, nutrients of 

 the food are separated. The proteids, carbohydrates and 

 salts, are taken up by the capillaries, while the fat of the 

 food, emulsified, is taken up by the lacteals. The contents 

 of the capillaries move on through the portal vein to the 

 liver, and thence on to the right side of the heart, while 

 the contents of the lacteals find their way into a long lym- 

 phatic tube beneath the backbone, which leads to what is 

 known as the thoracic duct, a large lymphatic vessel, which 

 opens into a big vein close to the first rib, which in turn 

 leads into the heart. From here the blood is forced to the 

 lungs to come in contact with air, and be oxydized, after 

 which it passes into the left side of the heart, from which 

 place it is distributed by means of the arteries to the 

 tissues throughout the body. The large artery, the aorta, 

 leads from the top of the heart along beneath the spine, 

 subdividing just below the hips. From here the arteries 

 extend on and down into the udder, one passing along by 

 the thigh bone (femur) and another to the extreme rear, 

 where, with considerable division and running together, 

 they continue on into and through the udder tissue. The 

 veins of the mammary glands converge at the base of the 



