Lactiferous ducts lead from the lobules of the mammary gland

Mammary gland

A mammary gland is an organ in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". In ruminants such as cows, goats, and deer, the mammary glands are contained in their udders...

 to the tip of the nipple

Nipple

In its most general form, a nipple is a structure from which a fluid emanates. More specifically, it is the projection on the breasts or udder of a mammal by which breast milk is delivered to a mother's young. In this sense, it is often called a teat, especially when referring to non-humans, and...

. They are also referred to as galactophores, galactophorous ducts, mammary ducts, mamillary ducts and milk ducts. They are structures which carry milk

Milk

Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

 toward the nipple in a lactating

Lactation

Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...

female.

Lactiferous duct:
the complex series of ducts is a system within the breast that drains into a main duct, the lactiferous duct, which ends at the nipple via a secretory pore. The large and intermediate ducts are lined by columnar epithelium supported by myoepithelial cells. Within the areola, the lactiferous duct dilates to form the lactiferous sinus in which milk accumulates in a nursing mother.
When a woman is not lactating,the lacterfeous duct is blocked by a keratin plug. This mechanical barrier prevents bacteria from entering the duct in non-lactating women.