46 MILK 



the same side of the cow, but no milk can appear in a left quarter 

 from a right quarter. 



The udder is a spongy organ consisting of skin, muscle, nerves, 

 veins, arteries, lymphatics, milk-ducts, secreting glands, and 

 fibrous fatty and connective tissue (Fig. 11). The size of the 

 fully developed udder is 24 to 54 by 16 to 32 by 10 to 20 cm. 

 The outer skin of the udder is soft and thin and is supported by 

 fibrous tissue. It is covered with hair which is softer than the 

 hair of the coat of the animal. The udder swells considerably 

 when milk is accumulating and contracts while milk is removed. 



Fig. 12. A plaster-of-Paris cast of the interior of the teat and milk cistern of 

 one quarter of an udder (Moore and Ward). 



The degree of contraction varies, and is particularly small when 

 the udder contains much fatty tissue. 



At the lower extremity of the udder are the teats, which are 

 tube-like appendages, and are 6 to 10 cm. long. There is one 

 teat for each quarter of the udder (Fig. 12). A sphincter muscle, 

 located at the end of the teat, keeps the milk from flowing from 

 the udder until it is relaxed by sucking or milking. The cow 

 has no voluntary control over this muscle. Sometimes, however, 

 the muscle is weak and milk leaks from the udder under the press- 

 ure of the accumulating secretion. On the other hand, the muscle 

 is occasionally so tight that a smooth, wooden wedge has to be 



