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Show 24 DR. E. LONNBERG ON DIGESTIVE [Jan. 14, It is thus evident that the contents of the ileum must pass into the colon, and from there, when the sphincter mentioned above relaxes, into the caecum. It is also evident that no large pieces can pass through the narrow opening into the caecum. A comparison between the contents of the colon proves this statement completely. A sample of the contents of the colon taken 2 cm. from the ileo-caecal valve consists chiefly of large pieces of the chitinous integument of insects, setae of such animals, etc. A sample from the caecum consists only of the tiniest particles which cannot be measured or identified. The narrow opening between the caecum and the colon serves accordingly as a filter. The large indigestible remains are kept back in the colon, the fluid and the fine particles suspended in the same pass into the caecum, where, no doubt, an absorption of the fluid takes place, after which the indigestible remains are forced back to the colon to be expelled with the faeces. The function of the caecum may thus be termed absorbing and desiccating. The large intestine acts nearly in its whole extent as a rectum, as the faecal matter is already formed into balls at a distance of only 2 cm. from the ileum (text-fig. 6). Text-fig. 6. Caecum of Petaurus breviceps. c, caecum; i, ileum; co, colon. Valvula Ueo-colica is seen to protrude into the colon, and a bristle is inserted through the narrow opening of the cseco-colic sphincter. In Phalanger, on the other hand, it can be assumed with certainty that the caecum has a digestive function, which may be concluded from the fact that it is provided with large glands. The great length of the colon makes it probable that it has digestive as well as reabsorbing powers. The dimensions of the different tracts of the intestine in a marsupial young of Petaurus breviceps, measuring 63 m m . in total length without tail, were as follows:-Small intestine 185 m m caecum 17 mm., and large intestine 43 m m , If these measurements be compared with those of the young animal itself (without tail) the relation is expressed by the following percentages --290 26, and 68. From this it may be seen that all three parts are |
