MARSUPIALS IN GENERAL. 7 
its name, the only exceptions to this rule being the instances 
where the pouch itself is absent. Showing at first but little 
signs of life, the young Marsupials hang on to the nipples of 
their parents till they have attained a state of development 
permitting them to move and perform the other ordinary 
functions of life; they may, however, as among the Kan- 
garoos, still make use of the pouch as a place of refuge till 
they attain dimensions which prohibit their entrance. It will 
be inferred from the above that the placenta or vascular organ 
connecting the blood-vessels of the foetus with those of the 
parent in the higher Mammals is totally wanting among the 
Marsupials, whence they are often spoken of as Implacentals, 
in contradistinction to the Placentals, or higher Mammals. 
With the exception of the Thylacine, where they are rudi- 
mentary, Marsupials are further characterised by the presence 
of a pair of so-called marsupial, or epipubic bones, attached 
to the front edge of the middle of the lower part of the pelvis. 
It was at one time supposed that these bones bore some special 
relation to the pouch, but, since they are present in both sexes, 
it is obvious that such cannot be the case. 
Among other features common to all Marsupials, it may be 
mentioned that the brain is relatively very small in proportion 
to the size of the head and body, while its external surface 
exhibits comparatively few foldings and convolutions ; thus 
indicating that the brain-power and general intelligence of 
these creatures is of a low grade. Another indication of their 
low organisation is afforded by the structure of the uterus of 
the female, which is double throughout its length, whence the 
name of Didelphia has been applied to the group. Another 
very characteristic feature is the inward inclination or inflec- 
tion of the lower border of the angle, or hinder extremity of the 
inferior edge, of the lower jaw. 
In all cases there are two pairs of limbs, which are norma] 
