MÀ s i, LY 
of the Mammary Organs of the Kangaroo. 73 
muscular contraction for the purpose of compressing a gland, 
and thereby emptying its ducts of their contents, we have 
already sufficient proof. The venom of the Rattle-snake is 
forced through its perforated fang by a muscular apparatus 
connected with the secreting organs; and the musk gland of 
the Crocodile has been shown by my friend Mr. Bell* to pos- 
sess a muscular investment, obviously destined to perform the 
same functions as I have attributed to a similar peculiarity of 
structure in the Kangaroo. 
The use of a forcible compression of the mammary gland of 
| the Kangaroo, exerted at the will of the mother for the purpose 
of ejecting its secretion, will be rendered apparent by an ex- 
amination of the young at the time it is first attached to the 
nipple; for the imperfect state of organization in which we find 
the young of marsupial animals at the time they first make their 
appearance in the pouch,—more particularly evinced by the 
state of the mouth and its appendages,—compared with the 
more mature development of the same parts in the young of 
other mammalia, renders some provision necessary, by which 
nutrition should be imparted solely by the agency of the mother ; 
and this provision is clearly afforded by the injection of the 
milk into the mouth by the means I have already mentioned, 
instead of that fluid being extracted by the suction of the young, 
as in the case of other mammiferous animals. ‘That the secretion 
of the marsupial mammary gland may be ejected by pressure 
made upon the part, is rendered probable not only by the exist- 
ence of a compressing muscle, but also by the structure of the 
marsupial teat and its proper investments, which I shall next 
describe. I wish it, however, to be clearly understood, that in 
the description which I am now giving of the anatomy of these 
parts, I refer to the mammary organ in the full-grown Kan- 
* Phil. Trans. 1827, p. 139. t. 11. 
VOL. XVI. L garoo, 
