Where in a cow's anatomy would you find an alveolus?

An alveolus is a small, sac-like structure that is primarily associated with the udder of a cow. In the context of dairy cattle, alveoli are the functional units within the mammary gland responsible for the production and secretion of milk. Each alveolus is lined with milk-secreting epithelial cells and is surrounded by capillaries and a myoepithelial layer, which aids in the contraction and expulsion of milk during milking or suckling.

The other options do not contain alveoli in the context used for milk production. The liver is involved in metabolism and other vital functions but does not have alveoli. The rumen and the stomach are parts of the digestive system designed for fermentation and digestion of feed rather than for milk production. Therefore, the udder is distinctly where alveoli are found, emphasizing its role in lactation and dairy production.