8 
MARSUPIATA. 
placental mammalia the angle of the jaw is almost invariably 
‘ on the same plane with the horizontal ramus. 
In addition to these points of distinction between the pla¬ 
cental and implacental or marsupial animals, there are others 
which are derivable from the number of the teeth. In die 
placental mammalia the normal number of incisors in both 
jaws is six, and of the true molars three on each side of each 
jaw, whilst in the present group no species has yet been found 
possessing six incisors in each jaw; the highest number 
found is in the Opossums of America, where there are ten in 
the upper jaw and eight in the lower: next follow the Dasyuri, 
in which they are eight above and six below; and in a great 
number of the species, as in the Kangaroo tribe, there are 
six above and two below. With the exception of the Wombat, 
which has two above and the same number below (as in the 
Rodents), there is no marsupial animal known possessing an 
equal number of incisors in tho upper and lower jaws. With 
the exception of the edentate species of Marsupials, or those 
which are nearly edentate, like the Tarsipes; and also except¬ 
ing tho Mynnecobius, all marsupialia possess four true molars; 
that is, four molar teeth on each side of each jaw, which have 
never replaced other teeth in the vertical direction—a number 
not clearly made out to bo found in any other group of qua¬ 
drupeds, but possibly may prove to exist in tho insectivorous 
quadrupeds forming the genus Can fetes. 
With regard to the structure of the molar teeth, they often 
correspond with the same teeth in the ordinary mammalia; 
when much complicated, as in the herbivorous, and especially 
tho insectivorous species, they present the four principal cusps, 
as in the placental herbivora and insectivora. In the Kangaroo- 
rats, these four cusps or tubercles are distinct, but in the true 
Kangaroos tho anterior and posterior pairs are joined, so as 
to present, before they are worn, two transverse sharp ridges. 
Resides the four* principal cusps, complicated molar teeth have 
