ALIMENTARY CANAL OF MARSUPIALIA. 411 



dense epithelium lines the inner surface of the latter tube : it is 

 continued over the capacious stomach to the pylorus, near which 

 orifice it is developed into numerous horny and sharp papilla?. The 

 subjacent mucous membrane is smooth ; the tunics of the stomach 

 are thin, to near the pylorus, where the muscular coat assumes 

 something of the gizzard-character, and the inner coat forms a pro- 

 minent protuberance in the duodenum. The intestinal canal of 

 the Echidna is seven times the length of the body; the mucous 

 membrane is not raised into valvular folds; a small vermiform 

 and glandular caecum divides the small from the large intestines; 

 the rectum terminates as in the Ornithorhynchus. 



The various modes of locomotion, resulting from the different 

 modifications of the osseous and muscular systems observable in 

 the several families of Marsupialia, relate to the acquisition of 

 as various kinds of alimentary substances, which necessarily re- 

 quire for their assimilation as many adaptations of the digestive 

 organs. Food — means of obtaining it — instruments for preparing 

 and mechanically dividing it — cavities, canals, and glands for 

 chemically reducing and animalising it — form a closely connected 

 chain of relationships and interdependencies. The preparatory 

 instruments have been described in previous sections. In all 

 Marsupials the oesophagus in passing through the chest recedes 

 from the spine as it approaches the diaphragm, and is loosely 

 connected with the bodies of the dorsal vertebrae by a broad 

 duplicature of the posterior mediastinum. In the Phalangers the 

 oesophagus terminates in the stomach almost as soon as it has 

 pierced the diaphragm ; in the Opossums it is continued some way 

 into the abdomen ; in the Didelphys virginiana, for example, for 

 the extent of an inch and a half ; in Did. brachyura, for half an 

 inch. In the Kangaroos the abdominal portion of the oesophagus 

 is of still greater extent ; I have observed it five inches long in a 

 male Macropus major. 



The inner surface of the oesophagus is generally smooth, or dis- 

 posed in fine longitudinal plaits ; but in the Virginian Opossum the 

 terminal part of the oesophagus presents many transverse folds of 

 the lining membrane analogous to, but relatively larger than, 

 those in the Lion and other Felines. I have not met with a like 

 structure in the Phalangers, nor in any other genus of Marsupials ; 

 what is more remarkable is that the transverse oesophageal rugae 

 are not developed in the carnivorous Dasyures or Phascogales, 

 where analogy would lead one to expect them, rather than in the 

 insectivorous Opossums. 



The stomach presents three leading modifications of structure 



