AUTHORITIES.--The above article is partly based on that of Sir W. H. Flower in the 9th edition of this work. The literature connected with mammals is so extensive that all that can be attempted here is to refer the reader to a few textbooks, with the aid of which, combined with that of the annual volumes of the _Zoological Record_, he may obtain such information on the subject as he may require: F. E. Beddard, "Mammals," _The Cambridge Natural History_, vol. x. (1902); W. H. Flower and R. Lydekker, _The Study of Mammals_ (London, 1891); Max Weber, _Die Säugethiere_ (Jena, 1904); W. T. Blanford, _The Fauna of British India--Mammalia_ (1888-1891); D. G. Elliot, _Synopsis of the Mammals of North America_ (Chicago, 1901) and _The Mammals of Middle America and the West Indies_ (Chicago, 1904); W. L. Sclater, _The Fauna of South Africa--Mammals_ (Cape Town, 1901-1902); W. K. Parker, _Mammalian Descent_ (London, 1885); E. Trouessart, _Catalogus mammalium, tam viventium quam fossilium_ (Paris, 1898-1899); and supplement, 1904-1905; T. S. Palmer, _Index generum mammalium_ (Washington, 1904); W. L. and P. L. Sclater, _The Geography of Mammals_ (London, 1899); R. Lydekker, _A Geographical History of Mammals_ (Cambridge, 1896). (W. H. F.; R. L.)
MAMMARY GLAND (Lat. _mamma_), or female breast, the organ by means of which the young are suckled, and the possession of which, in some region of the trunk, entitles the animal bearing it to a place in the order of Mammalia.
_Anatomy._--In the human female the gland extends vertically from the second to the sixth rib, and transversely from the edge of the sternum to the mid axillary line; it is embedded in the fat superficial to the pectoralis major muscle, and a process which extends toward the arm-pit is sometimes called the axillary tail. A little below the centre of the glandular swelling is the _nipple_, surrounding which is a pigmented circular patch called the areola; this is studded with slight nodules, which are the openings of areolar glands secreting an oily fluid to protect the skin during suckling. During the second or third month of pregnancy the areola becomes more or less deeply pigmented, but this to a large extent passes off after lactation ceases. In structure the gland consists of some fifteen to twenty lobules, each of which has a _lactiferous duct_ opening at the summit of the nipple, and branching in the substance of the gland to form secondary lobules, the walls of which are lined by cubical epithelium in which the milk is secreted. These secondary lobules project into the surrounding fat, so that it is difficult to dissect out the gland cleanly. Before opening at the nipple each lactiferous duct has a fusiform dilatation called the _ampulla_.