DIGESTIVE SYSTEM 13 1 



four and later three, but in the carnivora and cattle they are 

 entirely absent. In man the glands cease at the upper end of 

 the columnae rectales, and in place of the cylinder epithelium 

 stratified pavement epithelium is found. As regards the isolated 

 follicles, they are larger and more numerous in the large in- 

 testine than in the small intestine. 



The entire length of the large intestine, in the adult, as 

 compared with the small intestine is as I : 4. 



The two great glandular organs, the liver and the pancreas, 

 stand in closest relation to the digestive system, as may be 

 shown, ontogenetically and phylogenetically, from the in- 

 vertebrates up to man. The peculiar, often coloured, cells or 

 cell-groups, occurring in the intestinal epithelium of the worms 

 may be considered as the primitive rudiments of a liver. Such 

 gland formations are most highly developed in those worms 

 where the intestinal tube ramifies (Planarians) ; here too may 

 be mentioned the accessory glands peculiar to the intestine 

 of the Tunicata. The coloured cells of the inner surface 

 of the intestinal tube in the Echinodermata and, still more 

 markedly, the caecal appendix of the intestinal tube in the 

 star-fish secrete a bile-like fluid, though neither can be said 

 to possess a true liver in the sense of the liver of the higher 

 animals. The glands connected with the large intestine of 

 the arthropoda are admitted by all anatomists to be hepatic 

 glands. 



The gradual development of the liver may be traced in the 

 different classes of the mollusca. In the Brachiopoda and 

 Pteropoda, consisting still of a number of tubes, the liver ap- 

 pears in the Lamellibranchiata as an organ constructed of 

 acini and lobes surrounding the stomach and a great part of 

 the intestine. The liver of the Gastropoda is equally im- 

 portant, and in the Cephalopoda, in the form of a compact 

 gland with excretory ducts from the separate lobes, it has 

 already assumed the character of the liver of the vertebrates. 

 As in the invertebrates, the liver appears in its most primitive 

 form as a tube-like appendage of the intestine, so also in the 

 vertebrates, its development from the wall of the rudimentary 

 intestine may be traced in the embryo. In its simplest form 

 (as in the Amphioxus) it is a caecal appendix of the first 



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