THE SKIN. 



579 



nipple being absent. In the new-born infant the tubules branch 

 several times, and all of them show clavate termination. The 

 ramifications increase in number, in both sexes, up to the twelfth 

 year, without the production of acini, the main mass consisting 

 of connective tissue, destitute of fat-globules. 



At the time of puberty in girls the mammary gland develops 

 into a discoid body, composed of dense, fibrous connective tissue, 

 without fat 5 the radiat- 

 ing ramules exhibit in this 

 period acinous termina- 

 tions at the periphery of 

 the organ, and only here 

 is the lobular structure 

 marked. 



In pregnancy a con- 

 siderable development of 

 the acinous glands takes 

 place, especially toward 

 the end, when about 

 twenty ducts are found, 

 emptying at the point of 

 the nipple, and a corre- 

 sponding number of lob- 

 ules is produced by the 

 free ramification of the 

 ducts and the formation 

 of numerous acini within 

 one lobule. The ducts, before emptying, are widened into pear- 

 shaped sinuses j their lining throughout the ramification consists 

 of a single layer of columnar epithelium. The acini are lined 

 with cuboidal epithelia, and at the beginning of lactation exhibit 

 numerous fat-granules, both within the epithelia and the caliber. 

 (See Fig. 245.) 



In full lactation the lobules and the acini therein assume the 

 largest size j the epithelia are scarcely perceptible, for most of 

 them are transformed into fat, and upon being treated with tur- 

 pentine usually show the frame of cement-substance, the nuclei, 

 and numerous vacuoles (see page 332). After the period of 

 lactation has passed, the acinous structure of the gland re- 

 mains, the small acini surround the ducts in regular groups, and 

 the connective tissue now contains a large number of fat-glob- 

 ules. In the matron a few ducts only are found, lined with 



FIG. 245. ACINI OF THE FEMALE BREAST 

 AT THE BEGINNING OF LACTATION. 



CE, cuboidal epithelia ; F, fat-globules, both within 

 the epithelia and the caliber, stained black by osmic 

 acid ; CV, connective-tissue frame, with blood-vessels. 

 Magnified 600 diameters. 



