Arrangement of Milk Ducts. 5 



and is partially separated from the canal of the 

 teat by a more or less well - marked constriction 

 in the muscular walls of the upper part of the 

 teat. From the milk cisterns a system of canals 

 or so-called milk ducts extends to all portions of 

 the udder. These ducts are larger near their open- 

 ing into the milk cistern, and diminish in size 

 as they rise through the udder. They branch and 

 anastomose freely in all directions, and finally end 

 in a group of small sac -like bodies, the ultimate 

 follicles. The system of milk ducts arising from 

 each teat is practically distinct, though there is 

 more or less communication between the smaller 

 ducts in the upper portions of the two quarters 

 on the same side of the animal. This renders 

 it possible to draw a part of the milk secreted 

 in the hind quarter from the forward teat on 

 the same side, and vice versa. There is no com- 

 munication between the ducts on opposite sides 

 of the animal. At the junctions of the larger 

 ducts there are greater or smaller enlargements, 

 forming small cavities or milk reservoirs, which 

 serve the same purpose as the reservoirs at 

 the top of the teat. The branching points of 

 all the ducts, large and small, are guarded by 

 sphincter muscles. These muscles are connected 

 with the abdominal muscles of the animal, and she 

 is able to more or less completely close them at 

 will, and so "hold up" her milk. It requires a 

 strong effort on the part of the animal to com- 

 pletely close the larger ducts in the lower part of 



