524 
MR. OWEN ON THE MAMMARY GLANDS 
inch from the place of insertion it had evidently entered a central duct, down 
which it freely ran to the areola, where it escaped externally from one of the 
minute orifices just described. This process was repeated on most of the 
lobes with similar results ; the greater part of them terminated by a single 
duct opening exteriorly, distinct from the rest ; but in a few instances the 
ducts of two contiguous lobules united into one, and in these cases the mercury 
returned by the anastomosing duct, when the common one was tied up, and 
penetrated the substance of the other lobule as freely as that into which the 
pipe had been inserted. 
Some of the lobules injected by the reflux of the mercury through the anas- 
tomosing duct were dried, and various sections were submitted to micro- 
scopical examination. At the greater end the lobules are minutely cellular ; 
these cells become elongated towards the centre of the lobule, and as it grows 
narrower, form minute tubes which tend towards, and terminate in a larger 
central canal, or receptacle, from which the excretory duct is continued. When 
uninjected, the entire lobule might be readily supposed to be composed of mi- 
nute tubes; but it is difficult to imagine how the lobules can have been consi- 
dered as hollow csecums or elongated follicles. On making a section of the 
corium through the middle of the areola, the ducts were seen to converge in 
a slight degree towards the external surface ; but there was no trace of an 
inverted or concealed nipple, as has been observed in the kangaroo. (Fig. 5. 
PI. XVIII. represents a magnified view of this section, with a section of one 
of the dried and injected lobules.) 
The next stage of the inquiry was the examination of the ovary and other 
organs of generation in the specimens which had presented such a diversity of 
size in the mammary glands ; and as they exhibited in these dissections cor- 
responding differences of development, the following account of the structure 
of the uterine organs may not be wholly unacceptable, notwithstanding the 
extended memoir on the subject inserted by Professor Geoffroy in the M6- 
moires du Museum, tom. xv. p. 1. 
There is no part in the female Ornithorhynchus that can be properly termed 
vagina; but the canal which leads from the orifices of the uteri to the ex- 
ternal outlet may be divided into two portions : of these the first and most 
internal is termed by Professor Geoffroy the urethra-sexual canal, as it con- 
