THE MAMMARY GLAND. 441 



with elastic fibrils. This conjunctive tissue forms a supporting 

 framework for the milk-ducts traversing the nipple. The latter 

 show walls of rather dense fibrous tissue, with a large pro- 

 portion of elastic elements, and are provided with a lining 

 of one row of short cylindrical cells. As the external orifice 

 is approached, these cells begin to take on the character 

 of the ordinary epidermic corpuscles of the integument. 

 Partsch has found in many animals that the secreting paren- 

 chyma accompanied these ducts almost to their mamillary 

 orifices. 



The occurrence of unstriped muscle in the nipple, accords 

 with the fact of its erectile properties. But the exact mode of 

 distribution of these elements is still a matter of controversj^ 

 among histologists. From the researches of Winkler and 

 Kolessnikow, recently confirmed by Partsch, it would appear 

 that they occur not in the ducts themselves, but form an in- 

 complete ring around and external to the same. In or around 

 the smaller galactophorous ducts, muscle-cells cannot be unmis- 

 takably recognized, though some authors have described their 

 occurrence there. 



As regards the structure of these smaller galactopliorous 

 ducts (ductus lactiferi, milk-ducts) it is quite simple. Their 

 membranous walls consist of a delicate and closely woven 

 reticulum of connective tissue, with a large admixture of fine 

 elastic fibres. Henle, Meckel, and Kolessnikow have described 

 smooth muscle-cells in these canals, but, as already stated, 

 Partsch and others have denied their existence. At any rate, 

 on cross- sections the contracted condition of some of the larger 

 ducts results in a stellate appearance of their lumina, whereas 

 the smaller ducts always appear round or oval. 



The larger ducts traced into the gland tissue are found to 

 be provided with saccular dilatations immediately beneath the 

 nipple. These milk-reservoirs (sinus ductuum, lactiferorum, 

 sacculi lactiferi, or ampullcE) may be 5 to 8 mm. broad, and thus 

 become distinctly perceptible to the naked eye. Below these 

 dilatations the ducts again grow narrower, and by numerous 

 divisions and subdivisions form a system of ramifying tubes, 

 which terminate in the secreting alveoli. The structure of the 

 larger ducts does not materially differ from that of the smaller 

 ones. Their walls are, of course, considerably thicker, and 

 there is found in addition a greater proportion of elastic tis- 



