240 NORMAL HISTOLOGY. 



nar or flattened epithelium. The large excretory canals, the 

 galactophorous ducts, each of which collects the secretion from 

 an entire lobe, pass as distinct tubes to the nipple ; they possess walls 

 of considerable thickness, composed of fibrous and elastic connective 

 tissue, together with some unstriped muscle derived from the nipple. 

 The lining epithelial cells are columnar to within a few millimetres 

 of the external openings of ducts, where the epithelium becomes 

 stratified and continuous with the epidermis. The fifteen to twenty 

 excretory ducts, after a longer or shorter course, converge towards 

 the areola, within whose area they undergo considerable dilatation 

 to form the ampullae, which serve during lactation as temporary 

 reservoirs for the milk. 



The nipple consists, in addition to the external covering of pig- 

 mented and greatly wrinkled skin which is perforated at the tip by 

 the openings of the excretory milk-ducts, of a central mass composed 

 of the lactiferous canals and the blood-vessels embedded within 

 the fibro-elastic tissue. A considerable amount of unstriped mus- 

 cle exists, disposed as encircling and radiating fibres ; upon the 

 contraction of this muscle, which responds to mechanical stimulus, 

 the erectility of the nipple principally depends. The cutaneous 

 papillae are supplied with numerous nerve-terminations, which insure 

 a high degree of sensitiveness. The subcutaneous tissue of the 



nipple proper contains 

 no fat; around its base 

 and over the areola 

 elevations mark the 

 orifices of the scat- 

 tered groups of little 

 racemose structures 

 which constitute the 

 glands of Mont- 

 gomery. The in- 

 tegument of the 

 areola surrounding 

 the base of the nipple 

 usually possesses con- 

 siderable pigment, 

 the amount greatly in- 

 creasing during preg- 

 nancy ; large sweat- 

 glands and numerous well-developed sebaceous follicles are also 

 present within this area. 



The relative proportion of the glandular structure to the inter- 

 vening connective tissue varies with the condition of functional activity 



Section of human mammary gland undergoing retrogressive 

 changes after lactation : a, sections of ducts ; b, atrophic acini ; 

 c, fat-cells ; d, interlobular connective tissue. 



