236 POUCHED MAMMALS. 
animated lumps. Previous to birth there is no placental communication between 
the blood-vessels of the foetus and the parent; and at birth the rudimental young 
are transferred to the teats of the female, to which they adhere tightly for a long 
period, their lips being specially modified into a cylindrical sucking-organ. In 
most cases the young thus suspended are protected by a fold of skin on the 
abdomen of the female, which forms a pouch in which the teats are contained. 
From the universal absence of a placenta, these Mammals are regarded as forming 
a subclass of equal rank with the Placentals or Kutherians, and are spoken of as 
Implacentals or Metatherians; the latter term indicating their lower position, as 
compared with the Eutherian, or highest Mammals. 
The Placental, or Eutherian Mammals are, as we have seen, divided into 
numerous orders; and it may be thought that similar divisions could be instituted 
among the Implacentals or Metatherians. It happens, however,—so far at least 
as existing forms are concerned,—that this is not the case; but so as to render 
our classification symmetrical, it 1s necessary to have a name for the one order of 
Implacentals, the term Pouched Mammals, or Marsupials, has been selected, and we 
shall speak of these Mammals under either of these terms; it must, however, be 
constantly borne in mind that they also have the higher designation of Implacentals, 
or Metatherians, ranking with the term Placentals, or Eutherians. 
In addition to the primary distinction of the absence of a placenta, the 
Pouched Mammals present certain other more or less distinctive peculiarities. 
Mention has already been made of the general presence of a pouch, or marsupium, 
in which the abdominally-placed teats of the female are concealed; and to this it 
may be added that, with the single exception of the thylacine, the front brim of 
the pelvis always has a pair of divergent splint-like bones projecting forwards in 
the form of the letter V. These so-called marsupial bones—shown in all our 
figures of the skeletons of this group—were originally considered to be for the 
purpose of affording support to the pouch; but this view is discredited by their 
presence in both sexes. A peculiarity of the skull of all Pouched Mammals save 
one, is that the so-called angle, or lower posterior projection of the lower jaw, is 
more or less bent inwards, or inflected, as seen in the figure of the skull of Gray’s 
rat-kangaroo, given in the sequel. This peculiarity is not, however, distinctive of 
the order, since it also occurs in some of the Insectivores. The skull of every 
marsupial is further characterised by the presence of larger or smaller vacuities, or 
unossified spaces, in the bony palate. As regards their brains, it may be observed 
that all the Pouched Mammals display a low grade of organisation; the whole 
brain being small in proportion to the size of the body, while the foldings on the 
surface of its hemispheres are never of a very complex nature, and only developed 
at all in the largest members of the order. The reproductive organs of the female 
are likewise constructed after a lowly fashion; the oviducts always remaining 
perfectly separate from one another, and never uniting, as they do in so many of 
the Eutherian Mammals, to form a common chamber, or womb. 
Certain peculiarities connected with the number and mode of 
replacement of the teeth also aid in distinguishing marsupials from 
other Mammals. In the first place, as shown in the figure of the skull of the 
Tasmanian devil given later on, there may be more than three pairs of front or 
Teeth. 
