In this animal there are four teats, two of which, in the virgin state, are at the bottom of a narrow pouch in which they lie hid. It is to one of these teats that the marsupial foetus is attached immediately after its removal from the uterus, and their size, at first small in accord ance with the minute mouth of the animal, in creases with its growth. The muscular appa ratus above alluded to embraces both the teat and the gland, and acts from the marsupial as its fixed point. The teat is further provided with a true vascular erectile tissue.
The upper or smaller gland is perfectly similar in its organization to the larger, and, notwithstanding the doubts which Mr. Morgan expresses regarding its use, Mr. Owen observed in the instance which he has so carefully re corded in the Philosophical Transactions for 1834, that the foetus was attached to the upper and not the lower nipples, and " that the nipple in use by the young one of the previous year was the right superior or anterior one." With regard to their minute structure it would appear from the figures of Mr. Morgan that the lacteal tubes originate in plexuses and not in cells, but the text is not very precise on this point.
The consideration of the existence of these organs in those bird-like Mammalia, the Orui thorhynchi, or duck-billed moles of Australia, is interesting. For the beak-bearing mouth of the adult would not lead us to expect the ex istence of a gland, the secretion of which is usually obtained by the action of a soft mouth convertible into a sucking apparatus.
Nevertheless a distinct mammary gland was described and figured by Meckel in 1826; and an organization of the lips and tongue of the young animal to correspond with it was sub sequently described by Professor Owen in the Trans. Zool. Society, vol. i. p. 228, 1834.
According to Meckel this gland is placed on the side of the abdomen between the pan niculus carnosus, to which it adheres loosely, and the obliquus descendens abdominis,stretch ing from the anterior and external margin of the pectoral muscle and inferior extremity of the sternum to the thigh. Its great size is merely one among the many instances which we meet of the comparative want of con centration of individual organs in the lower as contrasted with the higher animals, for the secreting surface itself is much less extensive than in those animals in whom the whole organ is much less.
The mammary glands of the Ornithorhyn chus are peculiar for the absence of the nipple, a deficiency which is not met in any other class. In the Cetacea it is so completely bu ried and concealed that it has been described as absent, but it exists perfectly formed, buried in its protecting fissure. The defi ciency in the first and concealment in the last has a relation to the aquatic mode of life, the whole surface of the body being constructed with the view of avoiding friction. The mammary gland in the Ornythorhyncbus consists inter nally of pyriform ccecal pouches, with their bases turned towards the skin, their apices communicating with short excretory ducts ; the walls of these pouches are thick and the cavities nar row. As regards simplicity of the in ternal arrangement of the gland, that in the common porpoise, where the cells and milk tubes are large and diffused, may be placed next in order to the Orni thorhynchus.
There is no reason for supposing that there is any essential departure from this kind of arrangement of the secreting portion of the gland in dif ferent animals, the cellular or vesicular having been met with in all instances where this gland has been carefully injected and un ravelled. But the efferent ducts vary con
siderably. We learn from Sir A. Cooper that the cow, the ewe, the goat, the guinea-pig, and the porpoise, have only one tube in each teat. The pig has two, the rhinoceros has twelve, and the hare and rabbit and the cat and bitch several. " In the Graminivora the reservoirs are enormously large, in the Carni vora comparatively small. In the pig there is scarely any reservoir ; in the porpoise the great enlargement of the milk-tube is a substitute for the reservoir." Morbid analonly.—It must be clearly under stood by our readers that we do not intend to give more than a mere outline of its diseases, and must refer them for more ample information to the admirable works of Sir A. Cooper and others. The diseases of the breast have been divided by Sir A. Cooper into three classes; " first, those which are the result of common inflammation, whether it be acute or chronic. Secondly, into complaints which arise from peculiar or specific action, but which are not malignant, and do not contaminate other struc tures. Thirdly, into those which are not only founded on local, malignant, and specific ac tions, but which are connected with a peculiar and unhealthy state of the constitution." Simple inflammation of the breast, like in flammation in every organ where its progress would rapidly prove destructive to its essential structure, is attended with excessive and in ordinate pain, and this gives such warning of the danger that it cannot be disregarded by the sufferer. The fibrous protective covering of the gland,like that of the testicle, prevents inordinate swelling, but occasions greater hardness to the touch. This inflammatory action, usually very unequivocal in its appearance, very rapidly de velopes pus ; the abscess following is trouble some and extremely obstinate in cure ; chronic abscess does, however, occasionally occur, and absence of all the usual symptoms of inflam mation masks the character of the disease and gives rise to the suspicion that it is a malignant tumour requiring extirpation. Sir Astley re lates some cases which catne under his notice in which the sense of fluctuation indicated to him the true character of the disease, and others in which the extirpating knife of the surgeon was only arrested by the flow of pus. This same author describes such occasional distension of one of the lactiferous tubes caused by chronic inflammation and obliteration of its aperture as to simulate chronic abscess. The breast is liable to what has been called hydatid disease, of which there are four kinds, one of a malignant nature ; the other three are not so. The first has been designated by Sir A. Cooper cellulous hydatids ; the second is the sero-cystic tumour of Sir B. Brodie ; the third is the ani mal or globular. Cellulous hydatids are sim ple bags containing fluid. " The breast gra dually swells," says Sir A. Cooper,* " and in the beginning is entirely free from pain or tenderness; it becomes hard, and no fluctu ation can then be discovered in it ; it con tinues slowly growing for months and even years, sometimes acquiring very considerable magnitude, the largest I, have seen having weighed nine pounds; but in other cases, al though the bosom was quite filled with these bags, yet it never exceeded twice the size of the other breast." After a time fluctuation may be felt and the cutaneous veins enlarge, hut the breast continues free from pain and the constitution does not suffer. The tumour is moveable and pendulous, in some cases in volving the whole gland, in others only a small portion.