oe 
MARSUPIALIA. 327 
cessity for such a structure, for he dissected 
two small mammary feetuses of the Kangaroo 
for the especial purpose of showing the rela- 
tion of the larynx to the posterior nares. The 
epiglottis and arytenoid cartilages are elongated 
and approximated, and the rima glottidis ‘is 
thus situated at the apex of a cone-shaped 
Jarynx, (fig. 142, c,) which projects, as in the 
Cetacea, into the posterior nares, where it is 
closely embraced by the muscles of the soft 
palate. The air-passage (6) is thus completely 
Separated from the fauces, and the injected 
milk passes in a divided stream on either side 
the larynx to the esophagus. 
Fig. 142. 
SZ litt 
Md, 
Népple, and head of Mammary Fostus, Kangaroo. 
Thus aided and protected by modifications 
of structure, both in the system of the mother 
and its own, designed with especial reference 
to each other’s peculiar condition, and afford- 
ing, therefore, the most irrefragable evidence 
of creative foresight, the small offspring of the 
‘Kangaroo continues to increase, from suste- 
nance exclusively derived from the mother, for 
a period of about eight months. During this 
iod the hind legs and tail assume a great 
part of their adult proportions; the muzzle 
elongates; the external ears and eyelids are 
completed ; the hair begins to be developed at 
about the sixth month. At the eighth month 
the young Kangaroo may be seen frequently 
to protrude its head from the mouth of the 
pouch, and to crop the grass at the same time 
that the mother is browsing. Having thus 
acquired additional strength, it quits the pouch 
and hops at first with a feeble and vacillating 
gait, but continues to return to the pouch for 
occasional shelter aad supplies of food till it has 
attained the weight of ten pounds. After this 
it will occasionally insert its head for the pur- 
pose of sucking, notwithstanding another fetus 
may have been deposited in the pouch; for the 
latter, as we have seen, attaches itself to a dif- 
ferent nipple from the one which had been pre- 
viously in use. 
Mammary Organs—In the young Marsu- 
pial, as Mr. Morgan was the first to observe 
in the Kangaroo, the nipples are not visible, 
but are indicated by the orifices of a kind 
of cutaneous preputial sheath in which they 
are concealed. M. Laurent has noticed a 
similar condition of the nipples in a mam- 
mary feetus of an Opossum and a Perameles. 
I have also observed it in the marpmary foetus 
of a Petaurist and Dasyure: it is doubtless, 
therefore, common to all Marsupials. 
Once naturally protruded and the preputial 
sheath everted, the nipples, in the Kangaroo 
at least, continue external. They are longer 
and more slender than in other quadrupeds, 
and when in use generally present a terminal 
expansion (fig. 142, d). This part lies in 
a deep longitudinal fossa on the dorsum of 
the tongue (a, fig. 142); and the originally 
wide mouth of the uterine fetus is changed 
to a long tubular cavity, with a terminal sub- 
circular or triangular aperture just large enough 
to admit the nipple, to which the young Mar- 
supial thus very firmly adheres. 
In the Phascogale, in which the nipples are 
relatively larger than usual, and of a subcom- 
pressed clavate form, the young, when grown 
too large to be carried in the pouch, are 
dragged along by,the mother, if she be pursued, 
hanging by the nipples. 
The number of nipples bears relation in 
the marsupial, as in the placental Mammalia, 
to that of the young brought forth ata birth; 
although from the circumstance of the produce 
of two gestations being for a short time suckled 
simultaneously, the nipples are never so few. 
Thus the uniparous Kangaroo has four nipples ; 
of which the two anterior are generally those 
in use: the Petaurists, which bring forth two 
young at a birth, have also four nipples: the 
Thalycine has four nipples: the multiparous 
Virginian Opossum has thirteen nipples, six on 
each side and the thirteenth in the middle. In 
the Didelphys Opossum there are nine nipples, 
four on each side and one in the middle. The 
Didelphys dorsigera has the same number of 
nipples, although six is the usual number of 
young at a birth (fig.143). In the Phas- 
cogale penicillata there are eight nipples ar- 
ranged inacircle. The Perameles nasuta has 
the same number of nipples arranged in two 
slightly curved longitudinal rows; this Mar- 
supial has three or four young at a birth. 
The nipple in all the Marsupials is imper- 
forate at the centre; the milk exudes from six 
to ten minute orifices arranged round the apex. 
It increases in size with the growth of the 
mammary foetus appended to it. 
The mammary gland has the same essential 
structure as in the ordinary Mammalia; it has 
no cavity or udder; its chief peculiarity arises 
from its being embraced by the muscle, already 
noticed, which has the same origin and course 
as the cremaster muscle in the male. 
Marsupial pouch.—The development of the 
pouch is in an inverse ratio to that of the uteri 
and directly as that of the complicated vagine : 
thus it is rudimental in the Dorsigerous Opos- 
sum, which has the longest uteri and the sim- 
plest vagine: we may conclude therefore that 
the young undergo a greater amount of deve- 
lopment in the womb in this and allied 
species.* 
* Is there any essential modification of the mem- 
branes of the ovum in these small Marsupials? The 
means of determining this question are most de- 
sirable. 
