76 SECRETION. 



been verified and extended by Sappey, 1 are confined almost 

 exclusively to the secreting structure of the gland. The 

 interstitial tissue remains about the same, the blood-vessels, 

 only, being increased in number during lactation. As we are 

 treating of the mammary glands as secreting organs, a full 

 description of its structure is deferred until we come to con- 

 sider it in a state of functional activity. 



Structure of the Mammary Glands during Lactation. 

 Between the fourth and the fifth month of utero-gestation, 

 the mammary glands begin to increase in size ; and at term, 

 they are very much larger than during the unimpregnated 

 state. At this time the breasts become quite hard ; and the 

 surface near the areola is somewhat uneven, from the great 

 development of the ducts. The nipple itself is increased in 

 size, the papillae upon its surface and upon the areola are 

 more largely developed, and the areola becomes larger, 

 darker, and thicker. The glandular structure of the breasts 

 during the latter half of pregnancy becomes so far developed, 

 that if the child be born at the seventh month, the lacteal 

 secretion may generally be established at the usual period 

 after parturition. Even when parturition takes pi ace at term, 

 a few days elapse before secretion is fully established, and 

 the first product of the gland, called colostrum, is very dif- 

 ferent from the fully-formed milk. 



The only parts of the covering of the breasts that 

 present any peculiarities are the areola and the nipple. The 

 surface of the nipple is covered with papillae, which are very 

 largely developed near its summit. It is covered by epithe- 

 lium in several layers, the lower strata being filled with 

 pigmentary granules. The true skin covering the nipples is 

 composed of inelastic and elastic fibres, containing a large 

 number of sebaceous glands, but no hair-follicles nor sudori- 

 parous glands. According to Sappey, these glands, which 

 are from eighty to one hundred and fifty in number, are 

 always of the racemose variety, and never exist in the form 



1 SAPPEY, Traite $ anatomic descriptive, Paris, 1857, tome iii., p. 697. 



