Final answer:
The reservoirs for storing milk located behind the nipple are called lactiferous sinuses, which connect to lactiferous ducts and alveoli that produce and secrete milk.
Step-by-step explanation:
The reservoirs for storing milk located behind the nipple are known as lactiferous sinuses. These sinuses are an extension of the lactiferous ducts and connect to the glandular lobes within the breast, which contain clusters of milk-secreting cells called alveoli. The alveoli are responsible for the production of milk, which is then secreted into the ducts and stored in the sinuses before being drained through the nipple pores during breastfeeding.