One or both mammae may be absent. It is more frequent, however, to have supernumerary breasts or nipples, sometimes three, four, or even five, instead of two. The supernumerary breasts are usually situated near the axillae, or under the normal ones. But there are cases in which they have had a very abnofmal situation, as in the inguinal region, on the thigh, or even on the back. They are usually small in size, but in some cases they have produced milk during lactation. Supernumerary breasts are more frequent in males than females, and they occur preponderatingly on the left side. The occurrence of additional mammae is not altogether extraordinary, considering that in the lower animals the mammae are usually more in number than in man.