RODENTIA 447. 
stomach is much dilated, forming a large egg-shaped sac with 
thickened glandular walls; and in some other species, as in 
Lophiomys imhausi and in the Beaver, glandular masses are 
attached to and open into the 
cardiac or pyloric pouches. The 
alimentary canal (Fig. 196) of 
all Rodents, with the exception 
of the Dormice (J/yoridw), has 
a czecum, which is often of great 
length and sacculated, as in the 
Hares, Water-Voles, and Poreu- 
pines. In some instances, as in 
the Hamster and Water-Vole, 
the long colon is spirally twisted 
upon itself near its commence- 
ment. The liver is typically 
divided in all, but the lobes are 
variously subdivided in the 
different species (in Capromys \ 
they are divided into minute 
lobules); and the gall-bladder, 
though present in most, is absent 
in a few. In most species the Fie. 19.—Alimentary canal of Rat (Mus decu- 
penis (which is generally pro- puvwtty grater ort of th gm testo 
vided with a bone) can be more j, jteam: em, excum; ¢, colon. , 
or less completely retracted 
within the fold of integument surrounding the anus, where it lies 
curved backwards upon itself under cover of the integument. It 
may, however, be carried forward some distance in front of 
the anal orifice, from which in the breeding season, as in the 
Voles and Marmots, the prominent testicular mass separates it. 
The testes in the rutting season form projections in the groins, 
but (except in the Duplicidentata) do not completely leave the 
cavity of the abdomen. Prostatic glands and, except in the 
Duplicidentata, vesiculze seminales are present in all. The uterus 
may be double, each division opening by a separate aperture into 
a common vagina, as in Leporide, Seiurida, and Hydrocharus, or 
completely two-horned, as in most species. The mamme vary in 
number and position from the single abdominal pair of the Guinea- 
Pig to the ten thoracico-abdominal pairs found in some of the 
Rats. In the Octodontidw the mamm are placed high up on the 
sides of the body. 
The peculiar odour evolved by many Rodents is due to the 
secretions of special glands, which may open either into the 
prepuce, as in Jus, Arvicola, Cricetus, ete., or into the reetum, as in 
Arctomys and tulacodus, or into the passage common to both, as in 
