302 



MARSUPIALIA. 



bat, it is to the succeeding parts of the ali- 

 mentary canal that we have to look for those 

 modifications which should correspond 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 coecum 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 stomachy of the corresponding 

 group in the placental series. In the most 

 strictly carnivorous Fera, as the cat-tribe, there 

 is a ccecum, though it is simple and short; but 

 in the Marsupial Zoophaga this part is entirely 

 wanting, and the intestinal canal, short and 

 \vide,* 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 Entoraophagous 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 ccecum. 



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 ccecum, 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 coecum 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. 



Caecum of an 

 Opossum. 



l'ii cum <if the K.iala. 



''' The jpjunnm, in the Thylacine, has a dia- 

 meter of two inches and a half. 



of the way towards the blind extremity. 

 When we reflect that the Sloth, which has 

 the same diet and corresponding habits with 

 the Koala, has a singularly complicated sto- 

 mach, but no coecum, the vicarious office of 

 this lower blind production of the digestive 

 tube as a subsidiary stomach is still more 

 strikingly exemplified. What then, it may be 

 asked, is the condition of the ccecum in the 

 Marsupials with enormous sacculated sto- 

 machs ? It is in these species comparatively 

 short and simple. In the Potoroos which 

 scratch up the soil in search of farinaceous 

 roots, it is much shorter than in the great 

 Kangaroos which browze on grass. There is a 

 slight tendency to sacculation at the com- 

 mencement of the ccecum in the latter Mar- 

 supials, by the development of two longitudinal 

 bands (jig. 127). 



In the Wombat the ccecum is Fig. 127. 

 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 ccecum. 



The most interesting peculiarity 

 which the Zoophagous Marsupials 

 exhibit in the disposition of their 

 simple intestinal canal, consists in ^^ 

 its being suspended from the very Caecum of the 

 commencement of the duodenum Kangaroo. 

 on a simple and continuous me- 

 sentery, like the intestine of Fig. 128. 

 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 

 the lowest curve of the loop of the duodenum 

 to the right iliac region, as in the Kangaroos. 

 The intestine is a little narrower at its middle 

 part than at its two extremes; the tunics in- 

 crease in thickness towards the rectum. There 

 is a zone of glands at the commencement of the 

 duodenum. 



In the Entomophaga the duodenum is 

 tightly connected to the spine, where it crosses 

 to be continued into the jejunum : from this part 

 the mesentery is continued uninterruptedly 

 along the small intestines and colon to the 

 rectum; so that although the ccecum is gene- 

 rally found on the right side, its connections 

 are sufficiently loose to admit of a change of 

 position. 



In the Petaurus pi/gmtt.us the duodenum is 

 attached to the spine as in the Opossums, but 

 it is not tied down to the right iliac region by 



Ccectim (if (he 

 Wombat. 



