ANATOMY OF THE MAMMARY GLANDS. 327 



erties of the Meibomian fluid, except that it mixes in the form of an emulsion 

 with water more readily than the other sebaceous secretions. It is produced 

 in small quantity, mixed with mucus and the secretion from the ordinary se- 

 baceous glands attached to the eyelashes and the glands of the caruncula 

 lachrymalis, and smears the edges of the palpebral orifice. This oily coating 

 on the edges of the lids, unless the tears be produced in excessive quantity, 

 prevents their overflow upon the cheeks, and the excess of fluid passes into 

 the nasal duct. 



MAMMARY SECRETION. 



The mammary glands are among the most remarkable organs in the econ- 

 omy ; not only on account of the peculiar character of their secretion, which 

 is unlike the product of any other of the glands, but from the great changes 

 which they undergo at different periods, both in size and structure. Eudi- 

 mentary in early life and in the male .at all periods of life, these organs are 

 fully developed in the adult female only in the later months of pregnancy 

 and during lactation. In the female, after puberty, the mammary glands 

 undergo a marked and rapid increase in size ; but even then they are not ful- 

 ly developed. 



Physiological Anatomy of the Mammary Glands. The form, size and 

 situation of the mammae in the adult female are too well known to de- 

 mand more than a passing mention. These organs are almost invariably 

 double and are situated on the anterior portion of the thorax, over the great 

 pectoral muscles. In women who have never borne children, they gener- 

 ally are firm and nearly hemispherical, with the nipple at the most promi- 

 nent point. In women who have borne children, the glands during the 

 intervals of lactation usually are larger, are held more loosely to the sub. T 

 jacent parts and are often flabby and pendulous. The areola of the nipple, 

 also, is darker. 



In both sexes the mammary glands are nearly as fully developed at birth 

 as at any time before puberty. They make their appearance at about the 

 fourth month, in the form of little elevations of the structure of the true 

 skin, which soon begin to send off processes beneath the skin, which are des- 

 tined to be developed into the lobes of the glands. In the foetus at term 

 the glands measure hardly more than one-third of an inch (8'5 mm.) in di- 

 ameter. At this time there are twelve to fifteen lobes in each gland, and each 

 lobe is penetrated by a duct, with but few branches, composed of fibrous tis- 

 sue and lined with cylindrical epithelium. The ends of these ducts are fre- 

 quently somewhat dilated ; but what have been called the gland- vesicles do 

 not make their appearance before puberty. In the adult male the glands 

 are half an inch to two inches (12'7 to 5O8 mm.) broad, and ^ to of an 

 inch (2-1 to 6 - 4 mm.) in thickness. In their structure, however, they pre- 

 sent little if any difference from the rudimentary glands of the infant. 



As the time of puberty approaches in the female, the rudimentary ducts 

 of the different lobes become more and more ramified. Instead of each duct 

 having but two or three branches, the different lobes, as the gland enlarges, 



