Like hair, mammary glands are uniquely mammalian. These glands develop from distinctive mammary ridges running along both sides of the trunk of a mammalian embryo. Mammary glands are found in both sexes, but cease development in males well before puberty.
Mammary glands are probably highly modified sweat glands.
Milk teeth are probably not as efficient as adult teeth at chewing, due partly to their small size and partly to their ever-changing pattern of occlusion as the young mammal grows. This lack of efficiency is accommodated by reliance on a food that doesn't need to be chewed, milk. Evidence from the fossil record suggests that the earliest mammals probably were diphyodont, whereas late therapsids probably maintained the ancestral pattern of replacing teeth more than once. Mammary glands are made up of a system of ducts surrounded by glandular tissue, which secretes milk. Mammary glands differ somewhat in form from species to species of mammals.