MILK SECRETION. 23 
on the right side, and two on the left side. The divisions 
between the two glands on the side are not entirely complete. 
That is, there is enough connection between the two glands 
on the same side to allow a portion of the milk to be drawn 
from the rear teat to the front teat on the same side, and from 
Fic. 2—Schematic figure showing cross-section of cow’s udder; and also 
enlargement of epithelial cells in alveoli when cow is giving milk (1). Each 
alveolus is surrounded with a membrane called tunica propria. Cell 
nuclei not shown. When cow is in milk they are also enlarged. When 
not the epithelial!cells are flat and the nuclei small and spindle shaped (2). 
the front teat to the rear teat. The milk-glands proper are 
located near the abdomen and extend downwards into the 
udder a trifle. The remainder of the udder is filled with ducts, 
fibrous and connective tissue, muscle, nerves, and blood-vessels, 
the whole udder assuming a sort of spongy and open condition. 
