CHAPTER I. 



ANATOMY, PATHOLOGY AND HISTOLOGY OF THE 

 MAMMARY GLAND. 



Development and Gross Anatomical Structure. 



In the lowest form of mammalian life a group of glandular 

 ducts becomes differentiated from the glands of the skin in the 

 median abdominal region. These ducts exude their lacteal secre- 

 tions upon tufts of hair of the mammary region, from which it is 

 either licked or sucked by the young (duckbill, Ornithorhynchus 

 paradoxus). 



One of the land duckbills, the spiny anteater (Echidna hys- 

 trix), has lacteal ducts opening within an abdominal pouch 

 formed by a fold of skin of the mammary region in the shape of a 

 pocket, in which the young are protected and nourished during 

 their development. This abdominal pouch is not identical with the 

 tegumentary wall from which is developed the teats of higher 

 mammals, but it may be taken as the point of origin of the different 

 forms of teats. In higher marsupial animals the glandular ducts 

 are united into a complex gland with teats which constitute the 

 orifices of the confluent lacteal ducts. In other still higher species 

 the most varied kinds of gland structures are observed with 

 various forms of teat development. 



Among the higher mammalian forms the evolution of these 

 anatomical structures may be followed during embryonic life. 



On both sides of the body, between the anterior limb-bud and the inguinal fold, 

 the milk-ridge develops from a linear thickening of the ectoblast in the form of a ledge- 

 like elevation of the epidermis. Along this milk-ridge a series of at first spindle-shaped, 

 then round enlargements appear, which are separated by absorption of the intervening 

 portions of the ridge. These enlargements consist of masses of epithelial cells, which 

 correspond to the anlage, primordium or point of origin of the true mammary gland of 

 the lowest mammalia. This anlage sinks into the underlying mesoblastic tissue and 

 becomes surrounded by a proliferating integument, which forms an investment for the 

 growing epithelial mass. From this mammary envelope which becomes more or less flat- 

 tended the fibrous and muscular tissue of the areola and teat are derived. At its base, 

 solid epithelial sprouts grow out from the sides of the conical epidermal plug, later be- 

 coming the lactiferous ducts, while the club-shaped thickened extremities in the further 

 course of their development, form the milk sinus. Subsequently, the central part of the 

 ectoblastic ingrowth undergoes degeneration and what at first was an elevation, now be- 



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