ix THE SKIN AND CUTANEOUS GLANDS 503 



milk for a few days, which is popularly known as " witches' rnilk." 

 The mammary secretion may occur (though very rarely) in adult 

 males, in virgins, and in females who have not conceived, are not 

 pregnant, and not in labour. Talmud, Cardauo (1556), Fiorentino 

 (1553), A. V. Humboldt, Haeser, all cite authentic cases in which 

 the male gland secreted. Degeneration or involution of the gland 

 takes place in women after the menopause. 



During its maximal development, which coincides with the 

 period of suckling, the glandular mass of the female breast consists 

 of some twenty distinct lobes, held together by fibrous and areolar 

 tissue, interpenetrated by accumulations of adipose tissues. Each 

 lobe is a distinct gland, with a galactophorous or milk duct opening 

 by a separate orifice on to the summit of the mammilla. Before 

 branching, each milk duct dilates considerably to form an ampulla 

 or sinus, which serves as a temporary reservoir for the milk. Each 

 lobe divides into smaller lobes, and these again into lobules, con- 

 sisting of a collection of alveoli or terminal acini, into which the 

 minute lactiferous ductules open. The alveoli often present lateral 

 enlargements and sometimes (as in the pulmonary alveoli) com- 

 municate inter se by the breaking-down of the septa, so that larger 

 cavities are formed. 



The walls of the alveoli consist of a basement membrane, having 

 on its inner surface a layer of flattened stellate cells, which 

 embrace the gland cells like a basket. The glandular epithelium 

 is a single layer of cells, which vary considerably in form according 

 as they are at rest or active, whether the alveolus is dilated or con- 

 tracted, and so on. We shall subsequently return to the signifi- 

 cance of these differences. 



The secretory ducts have longitudinal fibres of plain muscle 

 continuous with those present in the skin of the nipple. For the 

 greater part of their course the ducts are lined with a single layer 

 of columnar cells, except the principal ducts which run to the 

 nipple, and are lined with scaly, stratified epithelium. 



The arterial vessels enter at different points and form a capil- 

 lary network round each alveolus; this is continued into veins 

 which surround the base of the nipple in Haller's circulus venosus. 

 The lympbatic vessels also, which directly convey the materials of 

 the lacteal secretion, surround the alveoli, and communicate with 

 numerous in tra- alveolar lymph sinuses containing a number 

 of leucocytes, some of which penetrate through the basement 

 membrane to the interior of the alveoli. The nerves running to 

 the mammary gland are branches of the intercostal and supra- 

 clavicular nerves. They proceed partly to the skin of the nipple, 

 partly to the muscular fibres of the ducts, the blood-vessels, and 

 the glandular acini where their endings have not yet been 

 determined. 



VII. Human Milk is a white or yellowish fluid, opaque, without 



