36 



Veterinary Obstetrics 



The mammae belong to the acinous type of glands and con- 

 sist fundamentally of the milk cells or acini, where the polyhe- 

 dral or spherical epithelial cells form the active secretory units, 

 and, from these, the milk is poured out through the small execre- 

 tory ducts into more extensive canals which serve as a common 

 outlet for a group of acini, constituting a lobule. 



These ducts continue to unite and form yet larger canals, which 

 are few in number and, according to species, empty either into 

 one, two or more milk cisterns or reservoirs in the teat, or, in 

 the absence of these, traverse the length of the teat to open by 

 separate orifices at the apex. Through these excretory ducts 

 the milk is drawn normally by the new-born animal by sucking ; 

 artificially, in dairying, it is forced out by compression with the 

 hand or other means in a manner closely analogous to the suck- 

 ing by the young. 



Areolar Zone 







Bloodvessels 



Fig. 4. Section through the mammary pit of a 20 cm. long fe- 

 male swine embryo after Prof 6. Magnified about 200. (Bonnet). 



The secretion of milk and its discharge from the udder bears 

 some analogy to the behavior of erectile organs. It has been as- 

 sumed by some that the milk is largely secreted and stored in the 

 galactophorous sinuses and cisterns during the intervals between 

 milking, but this is for the most part erroneous. The milk is chiefly 

 stored in the epithelial cells of the milk acini until, under excita- 



