808 
D I D E L P H I S. 
fupported upon a pair of mufcles which arife from thefe 
bones, and unite in the middle between them. The 
mammae are covered anteriorly by the lining of the falfe 
belly, and the nipples projeft into that cavity ; this co¬ 
vering is fimilar to the external Ikin, having a cuticle, 
and Ihort hair thinly fcattered over its furface, except at 
the root of the nipples, "where there are tufts of fome 
length, one at the bafts of each. There is alfo a ftrong 
mufcle that comes down from the upper part of the ab¬ 
dominal mufcles, and adheres firmly to each of the mam¬ 
mae; this mufcle, when the young is fucking, prevents 
the mamma being dragged from its natural fituation. 
The two bones which lie behind thefe mammae deferve 
a particular defcription, as they are peculiar to the opof- 
fum tribe, and belong both to the mammae and falfe 
belly, having no other apparent life but what is con- 
nefited with the motion of thefe parts. They are about 
two inches and an half long, and at their broadeft part 
meafure nearly half an inch ; they are attached to a pro¬ 
jecting part of the os pubis, fitted for that purpofe, juft 
before the infection of the redti abdominis mufcles ; this 
attachment to the pubis is by a very fmall furface, and 
admits of conliderable motion; they have likewife a 
connection by a ligament half an inch in breadth, to the 
ramus of the pubis, which joins the ilium. From their 
bafe, which is united to the pubis in thefe different ways, 
they become narrower till they terminate in a blunted 
point. The bones have a pair of mufcles infected into 
their bafe, to bring them downwards and outwards ; ano¬ 
ther pair into their blunted extremities to bring them 
forwards; a pair of broad flat mufcles fill up the whole 
fpace between them, arifing from their inner edge through 
its whole length ; they ferve as a fling to fupport the 
mammae, and alfo to bring the bones towards each other. 
Befides thefe additional bones, and the projection to which 
they are attached, there is another peculiarity in the 
ftruCture of the pelvis of the female kanguroo ; the two 
rami of the os ifchium, which join the pubis, have no 
notch between them, as in other quadrupeds, but form a 
rounded convex furface of fome breadth, projecting con- 
(iderably forwards; the furface itfelf is fmooth, like 
thofe over which tendons fometimes pafs; but the late¬ 
ral parts are rough, and have a pair of mufcles arifing 
from them inferted into the (kin of the falfe belly, to 
bring its mouth towards the pudendum. The mode in 
which the foetus of the opoflum, and particularly ot the 
kanguroo, paffes from the uterus into the falfe belly, has 
been matter of much fpeculation ; and it has been even 
fuppofed that there was an internal communication be¬ 
tween this cavity and the womb ; but after the moft dili¬ 
gent fearch, there is no fuch paffage to be found. This idea 
took its rife from there being no vifible opening between 
the uterus and vagina in the unimpregnated ftate ; but 
fuch an opening being very apparent, both during preg¬ 
nancy, and after parturition, overturns this hypothefis ; 
for we cannot fuppofe that the foetus, when it has reached 
the vagina, can pafs out in any other way than through 
the external parts. That this is really the cafe, and that 
in this way it gets into the falfe belly, is highly probable, 
for the following reafons: the falfe belly has mufcles 
to bring its mouth as near as poflible to the opening ot 
the vulva, which does not appear neceffary for any other 
purpofe than that of receiving'the foetus. The bones 
belonging to the mammae and falfe belly have mufcles, 
which by their aftion will bring down both thefe parts 
towards the vulva, for which no other ufe can be afligned ; 
and thefe parts are fo much detached trom the abdominal 
mufcles, that this efteft can be produced during their 
adtion to expel the foetus from the uterus. The vulva 
of this animal has naturally an unufual projection, and 
the margin of the pelvis immediately before it is rounded 
and fmooth, fo as to admit of its moving ealily in that 
direction; and the aCtion ot opening the mouth of the 
falfe belly, will bring down the fkin, and allow the exter¬ 
nal orifice of the vagina to be thrown ftill further out, 
fo as to projedt more dire fitly over the mouth of the falfe 
belly in which the foetus is to be depofited. It is alfo to 
be obferved, that if the parts in their natural ftate are 
fitted for fuch an action, they will be ftill more fo at the 
period in which it is to be performed; fince in all ani¬ 
mals, at that particular time, there are changes going on 
to facilitate the expullion of the young in the way moft 
favourable for its prefervation. 
The fize of the foetus at the time it leaves the uterus, 
is not afcertained ; but it has been found in the falfe belly, 
attached to the nipple, not more than an inch and a quar¬ 
ter in length, and thirty-one grains in weight, from a mo¬ 
ther weighing fifty-fix pounds. In this inftance the nip¬ 
ple was fo fltort a way in the mouth, that it readily drop¬ 
ped out; we mud therefore conclude that it had been 
very recently attached to it. The foetus at this period 
had no navel firing, nor any fign of there ever having 
been one ; it could not be faid to be perfectly formed, 
but thofe parts which fit it to lay hold of the nipple were 
more fo than the reft of the body. The mouth was a 
round hole, juft lar^e enough to receive the point of the 
nipple ; the two fore-paws, when compared with the 
reft of the body, were large and ftrong, to enable it to 
keep its hold ; and the little claws were extremely dif- 
tinCl; while the hind legs, which are afterwards to be 
fo very large, were both lliorter and fmaller than the fore 
ones. Mr. Home alfo received from Mr. Lang, in the 
month of March 1795, a fcetus taken from the falfe belly, 
fmaller than any that had been met with before. It 
weighed only twenty-one grains at the time it was taken 
from the falfe belly, and was lefs than an inch in length. 
Its fore-paws, while of this fize, were equally well formed 
to appearance as in the fcetus above defcribed, and double 
the length of the hinder ones ; but the mouth had evi¬ 
dently lefs width. When, therefore, the foetus firft ad¬ 
heres to the nipple, the face appears to be wanting, ex¬ 
cept the round hole to receive it ; and as the jaws and 
lips grow, they cover a greater length of the nipple, and 
give the mouth a better hold ; the upper furface of the 
tongue, as that organ grows, is concave, adapting it to 
the nipple which lies upon it, and from which it is de- 
ftined to receive its fuftenance. This mode of nourilhing 
the young in the opoffum tribe, refembles, in fome re- 
fpeCts, what takes place in the dog-fifh, whole egg is de¬ 
pofited in the oviduct, and hatched there. The yolk 
alfo of the egg in the bird-kind, being conveyed into the 
belly at the time of its being hatched, made.Mr. Home 
defirous to fee if any of the gelatinous fubftance of the 
uterus was conveyed into the belly of the young kangu¬ 
roo, but he could not, on diffeCtion, find any fuch ap¬ 
pearance ; and as it is to be immediately attached to the 
nipple, there feems no neceftity for fuch a provifion. If, 
therefore, we confider the varieties which occur in the 
formation of different animals as fo many parts of the 
fame fyftem, the mode of generation juft defcribed will 
be found, in this chain of the gradations of nature, to 
form a link between animals whofe young are nourifhed 
by means of a navel-ftring connected with the uterus, 
and thofe that are nouriflted independent of it. This 
link evidently confifts in the foetus being expelled from 
the womb immediately on becoming quick with life, and 
when a regular fupply of nourifhment is required for its 
enlargement and growth : with this view it is conveyed, 
by a peculiar aCtion of the parts, into the falfe belly, 
where the teats are placed ; and there by a moft wonder¬ 
ful inftinct of nature, and even before the external fea¬ 
tures are completely evolved, the almoft lifelefs foetus is 
directed to apply the minute orifice of its mouth to the 
nipple, which it takes in and fallens to by fuCtion ; thus 
receiving regular and equable nourifhment, as by a navel- 
ftring, until the little creature becomes fo far perfected 
and matured, as to be able to feek its food with the parent 
animal. 
In the annexed engraving, the fucking fcetus of the 
kanguroo is (hewn at different ftages of its growth. Fig. 3, 
exhibits 
