MILK SECRETION 



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to the amount and quality of the blood circulating 

 through the udder each day. 



The course taken by the blood is along the principal 

 artery (aorta) leading the blood away from the heart. 

 This main artery branches periodically in order to 

 supply the various organs with blood, but the branch 

 leading the blood to the udder passes along backwards 

 to the hind quarters, then in a downward direction 



Alveolus or sac. 



Small lobes (lobules) of alveolus. 



Muscles under the control of the cow 

 (voluntary). 



Milk-duct (Ductus lactiferonus). 

 Milk cistern. 



Muscles not controllable by the cow 

 (involuntary). 



Milk outlet of teat. 



Structure of a Quarter. 



along the thigh until it enters the mammary gland, 

 inside which it divides in the usual way into a large 

 number of very fine blood-vessels (capillaries) with 

 very thin walls. The capillaries practically mat them- 

 selves round the alveoli, and in this way the alveoli are 

 able to absorb from the blood any nutrient material 

 which they require for the manufacture of milk. These 

 capillaries gradually join up again as they leave the 

 front part of the udder, into a large blood-vessel called 

 the " milk vein," which follows the lower part of the 



