552 MANUAL OF HISTOLOGY. 



by ordinary cubical or polygonal cells about 0*0113 mm. in diameter (fig. 



540). 



It is an interesting fact, that here also that well-known network of very 



delicate tubules already mentioned ( 195) may be rendered visible by in- 

 jection, between the cells in the interior of 

 the acini (Gianuzzi and Falaschi). Accord- 

 ing to Langer, however, no fibrous network 

 can be discovered within the gland vesicles. 

 The excretory ducts terminate amid the 

 wrinkles of the mamilla with orifices about 

 0'7 mm. in diameter. Following them up 

 into the gland, we find them traversing 

 the mamilla in the form of tubes measuring 

 from 1-1 to 2-2 mm. across. At the base 

 of the nipple they become dilated into 

 what are known as the sacculi lactiferi, 

 diverticula of from 4 -5 to 6*8 mm. in trans- 

 verse measurement. After this they then 

 become narrowed again to 2 -2-4 '5, and con- 

 tinue their course with rapid ramification 



F*. 540.-Gland vesicles from suckling d Wn to the ultimate Vesicles. 



woman, showing cells and capillary The excretory canals of the lactiferous 



system present a lining of columnar cells. 



Their walls are composed of connective-tissue and a layer of elastic 

 fibres lying internally, and possibly also a few muscular elements occur 

 here, as they are to be found around the lobules (Henle). 



Both the nipple and areola, however, remarkable for their dark colour 

 and contractility, are possessed of these unstriped muscular fibres in 

 abundance. In the former are *to be found principally transverse bands 

 intersecting each other, while longitudinal bundles are of less frequency. 

 The arrangement of the bundles in the latter is chiefly circular, these 

 being again crossed by radiating bands (Henle). The mamilla contains 

 numerous papillae, and the areola sebaceous glands. 



It may be well to turn now for a moment to the development of the 

 organ. 



Like other glands connected with the skin ( 200), the mamma takes 

 its origin from the corneal germinal plate in the form of a growth inwards 

 of the cells of the latter. In the fourth or fifth month of intra-uterine 

 life it may be found as a solid mass of flattened globular or knobbed 

 figure, enveloped in the fibrous layer of the skin, and consisting of cells of 

 the rete Malpighi (Koelliker, Langer). A few weeks later (fig. 541) we 

 remark that the knobbed process (a) has given off new solid buds (b, c) 

 through cell proliferation. These are the first rudiments of the ducts of 

 the primary lobes, and are distined to further gemmation (c). Up to the 

 time of birth (fig. 539, 3), however, the rudimentary vesicles have not 

 been formed. During all this time the border is always more highly 

 developed than the central portions, as we might infer from the diskoid 

 figure of the gland, and this continues to be its condition until the end 

 (Langer). The ducts of the mammary gland of the infant present fibrous 

 walls lined with small cells. At their ends we find solid aggregations of 

 cells of irregular shape, the formative material for farther ramification. 



Even during childhood, and in girls (fig. 539, 4) as well as boys (5), 

 the development of terminal vesicles has not yet begun ; the canals con- 



