1268 



SPLANCHNOLOGY 





to twenty; they are termed the tubuli lactiferi. They converge toward the areola, beneath 

 which they form dilatations or ampullae, which serve as reservoirs for the milk, and, at the base 



Fat 



Lobule w 

 ravelled 



Lactiferous 

 tubule 



Alveoli 



Fat 



Duct 



Ampulla 



Lobules , 



Lbculi in connective 

 tissue 



FIG. 1172. Dissection of the lower half of the mamma during the period of lactation. (Luschka.) 



of the papillae, become contracted, and pursue a straight course to its summit, perforating it 

 by separate orifices considerably narrower than the ducts themselves. The ducts are composed 

 of areolar tissue containing longitudinal and transverse elastic fibers; muscular fibers are entirely 



absent; they are lined by columnar epithe- 

 lium resting on a basement membrane. 

 The epithelium of the mamma differs ac- 

 cording to the state of activity of the 

 organ. In the gland of a woman who is 

 not pregnant or suckling, the alveoli are 

 very small and solid, being filled with a 

 mass of granular polyhedral cells. During 

 pregnancy the alveoli enlarge, and the cells 

 undergo rapid multiplication. At the com- 

 mencement of lactation, the cells in the 

 center of the alveolus undergo fatty degen- 

 eration, and are eliminated in the first milk, 

 as colostrum corpuscles. The peripheral 

 cells of the alveolus remain, and form a 

 single layer of granular, short columnar 

 cells, with spherical nuclei, lining the base- 

 ment membrane. The cells, during the 

 state of activity of the gland, are capable of forming, in their interior, oil globules, which are 

 then ejected into the lumen of the alveolus, and constitute the milk globules. When the acini 

 are distended by the accumulation of the secretion the lining epithelium becomes flattened. 



The fibrous tissue invests the entire surface of the mamma, and sends down septa between 

 its lobes, connecting them together. 



The fatty tissue covers the surface of the gland, and occupies the interval between its lobes. 

 It usually exists in considerable abundance, and determines the form and size of the gland. There 

 is no fat immediately beneath the areola and papilla. 



Vessels and Nerves. The arteries supplying the mammae are derived from the thoracic 

 branches of the axillary, the intercostals, and the internal mammary. The veins describe an 

 anastomotic circle around the base of the papilla, called by Haller the circulus venosus. From 

 this, large branches transmit the blood to the circumference of the gland, and end in the axillary 

 and internal mammary veins. The lymphatics are described on page 715. The nerves are 

 derived from the anterior and lateral cutaneous branches of the fourth, fifth, and sixth thoracic 

 nerves. 



FIG. 1 173. Section of portion of mamma. 



