2030 



HUMAN ANATOMY. 



At first they are small and much like the terminal compartments of the gland and 

 lined with a thin stratum of longitudinally disposed involuntary muscle, upon which 

 rests a single layer of cuboid epithelial cells. The latter give place to cells of col- 

 umnar type within the lactiferous 



Excretory duct 



Involuntary 

 muscle 



Iveoli 



Interalveolar 

 stroma 



»— •*" 



Section of mammary gland before lactation. X 170. 



Fig. 1 71 2. ducts that are formed by the 



junction of the smaller canals. 

 On approaching the base of the 

 nipple, beneath the areola, each 

 milk-duct presents a spindle-form 

 enlargement or ampulla { sinus 

 lactiferus), from 10-12 mm. long 

 and about half as wide, that 

 serves as a temporary reservoir 

 for the secretion of the gland. 

 Beyond the ampulla the duct 

 narrows to a calibre of little over 

 2 mm., passes into the nipple, 

 and ends, after traversing the lat- 

 ter parallel with the other ducts, 

 in a minute orifice from .5-. 7 

 mm. in diameter, at the summit 

 of the papilla. On gaining the 

 last-named point, the lining epi- 

 thelium of the duct assumes the 

 stratified squamous type of the 

 adjacent epidermis. Embedded 

 within the delicate but more or 

 less pigmented skin that covers their exterior, the areola and nipple contain well- 

 rgarked bundles of involuntary muscle, by the contraction of which the nipple becomes 

 erect and prominent, as after the application of mechanical stimulus. Within the 

 areola this contractile tissue forms a layer, in places almost 2 mm. thick, that encircles 

 the base of the nipple and is continued into its substance as a net-work of bundles, 

 between which the lactiferous ducts pass. Deeper longitudinal strands of unstriped 

 muscle occupy the axial portions of the nipple. 



Over both areola and nipple the skin is provided with large sebaceous glands, the 

 secretion of which is increased 



during lactation and designed Fig. 1713- 



for protection while nursing. 

 Sweat-glands are absent over 

 the nipple, but large and modi- 

 fied in the vicinity of the periph- 

 ery of the areola. The surface of 

 the latter is modelled, especially 

 towards the close of pregnancy, 

 by low rounded elevations that 

 indicate the positions of the sub- 

 cutaneous areolar or Montgom- 

 ery s glands. The latter are 

 rudimentary accessory masses of 

 glandular tissue, from 1-4 mm. 

 in diameter, that correspond in 

 their general structure with that 

 of the mammary glands. Their 

 ducts open by minute orifices 

 on the surface of the areola. 



Milk. — The fully estab- 

 lished secretion of the mammary gland (lac femininum) is an emulsion, the fatty milk- 

 globules being suspended in a clear, colorless, and watery plasma, the variations 

 in tint — from bluish to yellowish-white — depending upon the amount of fat. '^^'' 



_ Blood- 

 -vessels 



Oil 

 droplet 



Interalveolar 

 septum 



Section of mammarv gland during lactation, showing distended 



alveoli lined with fat-bearing cells. X lyo- 



The 



