LACTATION 555 



In the male mammal, as just mentioned, the manamse do not 

 usually function, though milk is occasionally produced in Man at 

 birth and at puberty, and more rarely at other times. Male 

 goats and sheep have been known to yield milk exceptionally, 

 and the same is also said to be the case with male rats ^ (see 

 p. 584). 



Structure of the Mammary Glands 



The mammary glands are composed typically of a number 

 of lobes, which are themselves divisible into lobules. Each 

 lobule consists of connective tissue in which the convoluted 

 ducts of the gland are bound together. If these ducts are 

 traced backwards they are seen to arise from groups of secretory 

 alveoli. If they are traced forwards they are found to unite 

 together to form the lactiferous ducts, which in the human i 

 subject are from fifteen to twenty in number, and open to the I 

 exterior by minute apertures through the teat. The -lactiferous ' 

 ducts at their point of origin from the lobular ducts are provided 

 with reservoirs in which the milk collects during the periods of i 

 glandular activity (i.e. during lactation). These reservoirs in ' 

 some animals are of a very considerable size (e.g. whales, as 

 described above). The duct walls consist of areolar tissue 

 containing some un striated muscle fibres. They are lined 

 internally by short columnar epitheUal cells which become 

 flattened in the proximity of the nipple. A quantity of fat 

 generally covers the surface of the gland, excepting the nipple. 

 This fat is connected both with the skin in front and with the 

 glandular tissue behind. Like the latter it is lobulated by 

 processes of areolar tissue. The nipple also is formed of areolar 

 tissue with unstriated muscle fibres. It is richly suppUed with 

 vessels which give it an erectile structure. The glandular 

 tissue also is plentifully supplied with vessels, which vary in 

 size according to the condition of the gland. The glands in 

 Man are innervated by branches from the anterior and lateral 

 intercostal cutaneous nerves. Sensitive papiUae are present on 

 the surface of the nipple, and around it there is a small area of 

 skin, on which the ducts of Uttle secretory glands open to the 

 exterior. 



' Wiedersheim, loc. cit. 



