OPOSSUM FAMILY. 
4G3 
The Opossums may at once be distinguished from other 
Mammalia by the great number of their incisor teeth, there 
being ten in the upper, and eight in the lower jaw. These 
teeth are arranged in each jaw nearly in the form of a semi¬ 
circle: in the upper jaw the two foremost incisors are rather 
longer than the rest, and are generally separated from them 
by a narrow space; their form is nearly cylindrical, but at 
the apex they are slightly dilated. The canine teeth are well 
developed, and those of the upper jaw are the larger. The 
premolars are two-rooted, compressed, and pointed, and have 
a small posterior talon. The true molars of the upper jaw 
are tliree-rooted, and have the crown of a triangular form, 
and tubercular: those of the lower jaw are longer than 
broad, and, when viewed from either the outer, or inner side, 
they present three prickly cusps, of which the middle cusp is 
the highest; the foremost of these cusps is single, whilst the 
others are double, and there are therefore five prickly cusps 
to each molar. With regard to the general form, these 
animals, for the most part, have very nearly the proportions 
of the Common Eat, excepting that they have the muzzle 
more elongated, and terminated in a distinct naked muffle. 
In the larger species the body is proportionately stout. The 
tail is almost always very long, nearly destitute of hair, ex 
cepting at the root, and covered by a scaly skin 1 : this organ 
is here (as in many other of the Marsupialia) prehensile. 
The feet are naked beneath, five-toed, and all the toes are 
furnished with moderate-sized claws, excepting the inner 
toe of the hind foot, which is clawless.—(See PI. 10, fig. 3). 
In the possession of a coecum, and in having ten incisor 
teeth in the upper jaw, the Didelphida agree with the 
Peramelidce ; the incisor teeth of the Opossums, however, 
1 Very minute scattered hairs only, are found on the tail ot the Opossums, 
excepting at the root, where the tail is usually clothed with fur like that on 
the body. 
