232 



NORMAL HISTOL OG Y. 



The Mammary Gland. — Each mamma consists of a group of about 

 twenty similar compound racemose glands, opening by distinct orifices 

 at the tip of the nipple, and separated and enclosed by fibrous tissue, 

 in which there is a variable amount of fat. At the edges of the 

 mamma this fibrous stroma becomes continuous with the tissues of 

 the superficial fascia in which the breast is situated. 



Each of the glands entering into the composition of the breast 

 possesses a single main duct, the " galactiferous duct," which is lined 

 with columnar epithelium, except near its orifice, where the strati- 



Fig. 208. 



\ 





Maturing ovum of physa (fresh-water snail). (Kostanecki and Wierzejski.) Above are the 

 two small cells resulting from the division of the first polar body. Below is the ovum, 

 the nucleus of which is dividing to form the second polar body. Near the centre of the 

 ovum is the nucleus of the spermatozoon, just above which is its (divided) centrosome 

 with surrounding radiations in the cytoplasm. When the second polar body has been 

 formed the chromosomes remaining in the ovum will be ready to participate with those 

 of the spermatozoon in the further development of the then fertilized egg. 



fied epithelium of the epidermis extends for a short distance into 

 its lumen. A little below the base of the nipple the duct presents 

 a fusiform dilatation, called the " ampulla," which serves as a reser- 

 voir for the comparatively small amount of milk secreted in the 

 intervals between nursings. 



The main duct branches in its course from the nipple into the 



