MILK AS A FOOD 27 



the wild pig four to six pairs. In animals such as man and 

 apes, with free upper extremities capable of carrying their 

 young in the arms, the glands are situated on the upper 

 part of the thorax. The same is true of the bat, sloth, and 

 other animals in which the front extremities are relatively 

 highly differentiated. 



In most quadrupeds the mammary glands are suspended 

 from the abdomen. Here the mammary glands are in a 

 single pouch of skin known as the udder. The udder may 

 contain from one to three teats on either side. In the cow, 

 which interests us especially, the udder contains four separ- 

 ate mammary glands and four teats. They are usually 

 spoken of as the four quarters of the udder. Each quarter 

 is separated by a fibrous partition from its neighbors, and, 

 as we shall see later, each quarter is largely independent. 

 Thus one quarter may dry up while the other three remain 

 functionally active; one quarter may be diseased while 

 the others may remain healthy. Tuberculosis frequently 

 affects one quarter of the udder, and the common inflam- 

 mations of the udder known as garget are often limited 

 to one quarter. 



The human mammary gland when fully developed has 

 the following structure: It consists of about twenty lobes 

 separated from each other by connective tissue partitions. 

 These lobes are again divided into a larger number of lob- 

 ules, and these in turn are composed of numerous irregu- 

 lar round or oval or even tubular alveoli. The alveoli are 

 provided with small excretory passages which unite to 

 form the smaller ducts, these in turn uniting to form the 

 larger ducts. 



The mammary gland, in other words, resembles a bunch 

 of grapes, and is therefore known technically as a com- 

 pound racemose gland. Each grape corresponds to an alve- 

 olus. The alveolus is the milk factory. The stem to each 

 grape represents the little duct which conducts the milk 

 from each alveolus to the large stem or main duct through 



