VIVIPAROUS ANIMALS. 397 
the third kind, termed Uterus duplex, the horns, instead 
of opening into a common cavity, enlarge each into a se- 
parate uterus, opening by a distinct aperture into the va- 
gina. This kind prevails in hares and rabbits. In the 
American opossum and wombat, the uterus is double, with 
an oviduct entering the summit of each cavity. Instead 
of the uteri terminating separately in the vagina, as in the 
hare, they unite to form a common necly or opening. 
From each side of this neck a canal arises, and, after a se- 
micircular course, terminates obliquely in the vagina. In 
the kangaroo, the uterus is simple, with a trace of a di- 
vision, by means of a longitudinal ridge on each side. The 
oviducts terminate in the summit, one on each side of the 
ridge. Near their termination on each side, a lateral canal 
arises, which terminates in the vagina. The uterus, with 
these lateral semicircular canals, has been termed Uterus 
anfractuosus. 
The Vagina is a short dilatable canal, the walls of which 
consist of cellular substance, supplied with bloodvessels, 
and lined, internally, with a soft mucous covering. At its 
origin it embraces the neck of the uterus, which usually 
projects a little, and whose opening is denominated os tin- 
ce, from a supposed resemblance to the mouth of a tench. 
It is considered as terminating at the orifice of the urthera, 
in the vulva, the common cavity opening externally, and 
exhibiting, in the different species, very remarkable pecu- 
liarities. 
The manner in which the uterine system is excited to 
action, so as to produce impregnation, appears to be in- 
volved in the deepest obscurity. Various conjectures have 
been proposed, and hypotheses advanced, in the absence 
of accurate observation or decisive experiment. That the 
impregnating fluid is conveyed through the uterus and 
oviducts to the ovarium, is rendered probable, by the 
‘ circumstance, that many of the eggs or germs of those 
