202 
bat, it is to the succeeding parts of the ali- 
mentary canal that we have to look for those 
modifications which should co nd with a 
vegetable, a mixed, or an animal diet; and 
never perhaps was a physiological problem 
more clearly illustrated by comparative ana- 
tomy than is the use of the caecum coli by 
_ the varying conditions which it presents in the 
present group of Mammalia. 
In the most purely carnivorous group of the 
Marsupial order the stomach presents in the 
magnitude of the left cul-de-sac a structure 
better adapted for the retention of food than 
we find in the stomachs of the corresponding 
group in the placental series. In the most 
strictly carnivorous Fere, as the cat-tribe, there 
is a cecum, though it is simple and short; but 
in the Marsupial Zoophaga this part is entirely 
wanting, and the intestinal canal, short and 
wide,* is continued, like the intestine of a rep- 
tile, along the margin of a single and simple 
mesentery from the pylorus to the rectum. 
In the Entomophagous Marsupials, some of 
which are suspected with reason to have a 
mixed diet, the intestinal canal is relatively 
longer; the distinction of small and large in- 
testine is established; and the latter division 
commences with a simple, moderate-sized, sub- 
clavate cecum. 
In the Carpophagous Pha- 
langers, whose stomach resem- 
bles that of the predatory Da- 
syure, the compensation is made 
by a longer intestine, but prin- 
cipally by the extraordinary 
length of the cecum, which ir 
some species is twice that of 
the body itself. 
Lastly, in the Koala, which 
is, perhaps, a more strictly ve- 
getable feeder than the Petaurists or Pha- 
langers, the cecum is more than three times 
the length of the animal, and its essential 
part, the inner secreting membrane is farther 
augmented by about a dozen longitudinal 
parallel, or nearly parallel, plaits, which 
are continued from the colon three-fourths 
Fig. 126. 
Fig. 125. 
Ceecum of an 
Opossum. 
Cacum of the Koala. 
* The jejunum, in the Thylacine, has a dia- 
meter of two inches and a half. 
MARSUPIALIA. 
of the way towards the blind extremi 
When we reflect that the Sloth, which hi 
the same diet and connate habits | 
the Koala, has a singularly complica’ dd 
mach, but no cecum, the vicarious offic 
this lower blind production of the dige: 
tube as a subsidiary stomach is still m 
strikingly exemplified. What then, it may 
asked, is the condition of the cecum in 
Marsupials with enormous sacculated _ 
machs? It is in these species compar 
short and simple. In the Potoroos 
scratch up the soil in search of f 
roots, it is much shorter than in 
Kangaroos which browze on grass. Ther 
slight tendency to sacculation at the 
mencement of the cecum in the latter | 
supials, by the development of two longitud: 
bands (fig. 127). 
In the Wombat the cecum is 
extremely short, but wide; it is 
remarkable for being provided 
with a vermiform appendage. 
In this animal, however, the 
colon is relatively longer, larger, 
and it is puckered up into sacculi 
by two broad longitudinal bands. 
In the specimen dissected by 
me, one of these sacculi was so 
much longer than the rest as to 
almost merit special notice as a 
second cecum. 
The most interesting peculiarit 
which the Zoophagous Staracpiale 
exhibit in the disposition of their 
simple intestinal canal, consists in 
its being suspended from the very 
commencement of the duodenum 
on a simple and continuous me- 
sentery, like the intestine of 
a carnivorous reptile. The 
duodenum makes the ordi- 
nary fold on the right side, 
but it is not tied to the spine 
at its termination; the com- 
mencement of the jejunum 
may, however, be distin- 
guished by a slight twist of 
the mesentery, and a fold of 
peritoneum is continued from Wombat. 
the lowest curve of the loop of the duoder 
to the right iliac region, as in the Kangar 
The intestine is a little narrower at its mic 
part than at its two extremes; the tuni 
crease in thickness towards the rectum. u 
is a zone of glands at the commencement of 1 
duodenum. 7 
In the LEntomophaga the duodenum 
tightly connected to the spine, where it eros: 
to be continued into the jejunwm : from this pai 
the mesentery is continued uninterruptec 
along the small intestines and colon to t 
rectum; so that although the cecum is ge 
rally found on the right side, its connections 
are sufficiently loose to admit of a 
position. i 
In the Petaurus pygmaeus the duodenum is 
attached to the spine as in the Opossums, but 
it is not tied down to the right iliac region 
es" 
ae. 
Fig.1 8. 
Cacum 
