— a — e —ÓÓÓCL n. iua 
— — 
of the Mammary Organs of the Kangaroo. 79 
the living animal, or by artificial injection after death. The exist- 
ence of this structure throughout the whole length of the marsu- 
pial teat, will at once account for the extraordinary enlargement 
of that part before alluded to; for since the veins of the plexus 
empty themselves into the mammary vessels, an obstruction to 
the circulation of blood through their main trunks must neces- 
sarily operate in producing a congestive swelling both of the 
marsupial gland and of the teat. I conceive, therefore, that the 
distention of the nipple at the period of suckling, is occasioned 
not only by the injection of its excretory ducts, but also by the 
state of venous congestion which must necessarily occur at that 
time in the vascular covering which surrounds those ducts, 
= occasioned by the pressure of the muscles of the marsupial 
gland upon the trunks of the veins returning blood from the 
part. Thus it will be understood, that the teat is composed 
of four distinct structures; first, of the common integuments : 
secondly, of its compressing muscle; thirdly, of the vascular 
plexus, which I have just mentioned ; and lastly, of its central 
fasciculus of lactiferous tubes. 
I have injected the excretory ducts of the gland with quick- . 
silver from the extremity of the nipple to their extreme branches, 
and have met with no unusual appearance either as regards 
their course or distribution. They are about twenty in number, 
and terminate by separate openings at the extremity of the nip- 
ple. The appearance which they present when injected is ac- 
curately shown (tab. 8. f.2.d.). They are bound together by 
a delicate tissue of reticular membrane, and are continued a 
short way into the substance of the gland before they sepa- 
rate. Throughout their whole course they are possessed of a 
very considerable degree of elasticity. - 
Having thus detailed the anatomical peculiarities which I 
have met with in the marsupial gland and teat, and having en- 
^ deavoured 
