Page:The American Cyclopædia (1879) Volume XI.djvu/91

 MAMMARY GLANDS MAMMEE APPLE 83 this immense lapse of time genera and species have changed, either that they have been newly created at the several epochs, or, as Darwin and others maintain, have been modified by pro- cesses of natural selection and development, many original and intermediate forms having become extinct, and, from the imperfection of the geological record, as yet having afforded no indication of their existence. None of the mammalian genera of the secondary epoch have been found in the tertiary ones; no genus of the older eocene has been discovered in the newer; very few eocene genera have been found in the miocene, and none in the pliocene ; many of the miocene genera are peculiar to that division, and some indistinguishable from existing species begin to appear only in the newer pliocene; while the perissodactyls and omnivorous artiodactyls have been gradually dying out, the true ruminants have been in- creasing in genera and species. One class of organs seems to govern one order, and another class another order; for example, the teeth, which are so diversified in marsupials and edentates, are remarkable for the constancy of their characters in rodents and insectivora; and as a general rule, the characters from the dental, locomotive, and placental systems are more closely correlated in the gyrencephala than in the two inferior sub-classes. MAMMARY GLANDS, the organs which secrete the nutritive fluid, milk, by which the young of man and the mammalia are nourished during the early periods of life. They vary from two in the human female to 10 or 12 in the lower mammals, and may be pectoral as in the former, or pectoral and abdominal, or only abdominal, as in the latter. Each gland is made up of a number of separate lobules, more or less closely connected by fibrous tissue and fat, and bound down by the same to the pectoral or abdominal muscles. The lactifer- ous tubes arising from the minute ultimate follicles of the lobules terminate in the mam- millary tubes of the nipple, 10 or 12 in the hu- man female, straight but of variable size; at the base of the nipple, and extending into the gland, are reservoirs for containing a constant supply during lactation ; these are often much larger in the lower animals than in woman. The skin covering them is very delicate and smooth ; the colored circle around the nipple is called the areola, which becomes darker during and after gestation; the irregular surface of the nipple is covered with a very sensitive skin, and much erectile tissue enters into its sub- stance. The tubes are lined with a very vascu- lar mucous membrane, which has its own secretion sometimes in considerable quantity. These glands, especially during lactation, are well supplied with blood from branches of the subclavian and axillary arteries; their nerves come from the brachial plexus and the inter- costals, and the sympathetic plexus accompa- nying the mammary arteries. The inner sur- face of the follicles is covered with a layer of epithelium cells, the real agents in the secreting process. They present no great difference in size in the sexes until near the age of puberty, when a considerable enlargement takes place in the female; from the increased supply of blood during 'gestation, there is a sense of ten- derness and distention which is one of the earliest and most valuable signs of pregnancy. These glands in the male are miniatures of those of the female, but the essential structure is the same, as is shown by the authentic cases in which they have become sufficiently devel- oped in men to produce a secretion of true milk. Though the functional activity of these glands is naturally limited to the period succeeding parturition, their secretion is sometimes seen in virgins and in aged women, in whom a strong desire to furnish milk and a continual irritation of the nipple by the infant's mouth have stimulated the organs to unnatural ac- tivity. The prolonged secretion of milk in domestic cows, which usually lasts for about ten months after calving, is simply a continued action of these glands due to artificial treat- ment. The presence of these organs has given the name to the mammalia, the highest class of vertebrated animals, implying a mode of intra-uterine and extra-uterine development not found in birds, reptiles, or fishes. Physio- logically these glands belong to the generative system, and are gradually removed from the caudal to the pectoral region, as we ascend from cetaceans to the human female ; the for- ward, outward, and upward direction of the nipples is exactly adapted to the position of the child lying in its mother's arms, and the greater abundance of the lactiferous tubes at the lower portion of the breast forms a soft cushion for its head to rest upon. In the African and sometimes in other races, after lac- tation, the skin covering the breasts becomes so lax, and the organs so elongated, that they can be thrown over the shoulders like bags. The mammary glands are subject to many painful and dangerous diseases, among which may be mentioned acute and chronic inflam- mations, abscesses, and encysted, fibrous, and cancerous tumors; they are sometimes enor- mously overloaded with fat. MAMMEE APPLE (mammea Americana), a handsome tree of 60 ft. in height, native of the Caribbean islands and the neighboring conti- nent. It has large, oval or obovate, shining, leathery, opposite leaves, white, sweet-scented flowers, and large, round, obsoletely three- or four-cornered fruit, which sometimes grows to the size of a child's head. The fruit is cov- ered with a double rind ; the outer is leathery, tough, and brownish yellow; the inner, thin, yellow, closely adhering to the flesh, which is firm, bright yellow, and of a singular pleasant taste and a sweet aromatic smell ; but the skin and seeds are very bitter and resinous. The pulp is eaten alone, or cut up into slices with wine and sugar, prepared as a jam or marma- lade, or with sirup. From the yellowness of