276 SPECIAL HISTOLOGY. 



exhibits a certain number (12 — 15) divisions, of which the 

 internal still approximate the rudimentary papilla, in fact 

 have either simple flask-like ends, or terminate in two 

 or three sinuosities; whilst the others are in connexion 

 with a greater number. The excretory duct of each of these 

 rudimentary lobules, which is either simple or possesses two 

 or three branches, is composed of a fibrous membrane of 

 immature, nucleated connective tissue, and an epithelium of 

 small cylindrical cells, and is manifestly hollow; whilst the 

 dilated ends, which cannot in this case, any more than in 

 other glands in the process of development, at this time be 

 termed terminal vesicles, are still solid ; being wholly composed, 

 besides the fibrous tunic continued upon them from the ducts, 

 of minute nucleated cells. From this very simple form, the 

 later one is thus developed : by the long continued gemmation 

 of the primary and subsequently formed, clavate ends, and 

 their simultaneous excavation, a much branched duct, beset 

 in its offsets with whole groups of hollow gland-vesicles, is at 

 last formed. These processes, however, go on more slowly in 

 the lacteal gland than in any other of the secretory organs. 

 According to Langer, to whom we are indebted for careful 

 researches upon this subject, true terminal vesicles are never 

 met with in childhood, before menstruation is established, but, 

 universally, only undeveloped ducts with clavate ends. On 

 the occurrence of puberty, true gland-vesicles are formed, but 

 at first only at the borders of the gland, until, ultimately, in 

 the first pregnancy, the entire gland is fully developed. After 

 the first lactation, it is true, the gland again diminishes in 

 size, but all its constituent parts remain, and again enlarge in 

 the succeeding occasions of conception, without the addition of 

 any new parts. At the period of involution — probably also, 

 if after a pregnancy, too long a time has elapsed without the 

 functions of the gland being called into play — it undergoes a 

 retrograde metamorphosis, until finally, in old age, all the 

 gland-vesicles have disappeared, and nothing but the more or 

 less persistent lactiferous ducts, with their epithelium in a state 

 of fatty degeneration, are to be found in the adipose cushion 

 which supplies the place of the glandular tissue. 



The milk, the secretion of the mammary glands, consists of 

 a fluid, the milk-plasma, and innumerable spherical, opaque 



