THE POUCHED MAMMALS, OR MARSUPIALS 1407 



vessels of the foetus and the parent, and at birth the rudimental young are trans- 

 ferred 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 fe- 

 male, 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 Eutherians, and are spoken of as Implacentals or Meta- 

 therians; 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 nu- 

 merous 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 exist- 

 ing forms are concerned, that this is not the case; but so as to render our classifi- 

 cation symmetrical, it is 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 Meta- 

 therians, 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 forward in the form of the letter 

 V. These so-called marsupial bones shown in all our figures of the skeleton 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 pecul- 

 iarity 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 inward, or in- 

 flected. 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 charac- 

 terized 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 organization; the whole brain being small in pro- 

 portion 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 mem- 

 bers 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 re- 

 placement 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 Tas- 

 manian devil given later on, there may be more than three pairs of front or incisor 

 teeth in the upper jaw, and in such cases the number of pairs of these teeth in the 



