TYPES AND MARKET CLASSES OF LIVE STOCK 



159 



The arterial circulation. The mammary glands are abun- 

 dantly supplied with blood. The blood leaves the heart through 

 the posterior aorta, common iliacs, and external iliac, which 

 carry backward to the region of the hips. The external iliac 

 there divides into two arteries, one of which, the prepubic, divides 

 into the two pudic arteries, the external one of which passes 

 down the thigh and gives off a branch, known as the mammary 

 artery, which enters the top of the udder from the rear. The 

 mammary artery has four large branches, one for each quarter 

 of the udder, and there is also a small branch for each rudi- 

 mentary gland. The large branches subdivide within the 

 gland tissue. 



Fig. 49. Circulation To and From the Udder. 



The broken lines represent the arteries which carry blood containing the 

 nutritive material to the udder where it is manufactured into milk. The 

 heavy black lines represent the veins which carry the blood back to the heart. 

 Note that there is but one route from the heart to the udder, whereas there 

 are two routes from the udder to the heart. M. V., milk-vein; M. W., milk- 

 well. (After Bitting of the Indiana Station.) 



The venous circulation is more complex than the arterial. 

 The blood is collected from the capillaries by from 14 to 17 

 large veins which empty into the mammary vein running parallel 

 with the mammary artery at the top of the udder. The mam- 

 mary vein is divided into two parts which encircle the top of 

 the udder and connect in front and behind like a rope tied around 

 it. From this circuit of veins the blood returns to the heart by 

 two routes. One route leads out to the rear of the udder, then 



