Arrangement of Milk Ducts. 5 
as the milk cistern, serving to hold the milk 
after its secretion until it is drawn. It is of 
varying capacity, though it seldom holds more 
than half a pint. From the milk cisterns a system 
of canals or so-called milk duets extends to all 
portions of the udder. These ducts are larger near 
their opening 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 be- 
tween 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 communication between the ducts on opposite 
sides of the animal. At the junctions of the 
larger ducts there are greater or smaller enlarge- 
ments, 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 
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