DIGESTION. 



119 



Fig. 18. 



\ 



commencement (Fig. 18), we find the cavity of the mouth, which is 

 guarded at its posterior extremity by the muscular valve of the 

 isthmus of the fauces. 

 Through the pharynx and 

 oesophagus (a), it commu- 

 nicates with the second 

 compartment, or the sto- 

 mach (b), a flask-shaped 

 dilatation, which is guarded 

 at the cardiac and pyloric 

 orifices by circular bands 

 of muscular fibres. Then 

 comes the small intestine (e), 

 different parts of which, 

 owing to the varying struc- 

 ture of their mucous mem- 

 branes, have received the 

 different names of duode- 

 num, jejunum, and ileum. 

 In the duodenum we have 

 the orifices of the biliary 

 and pancreatic ducts (/, g). 

 Finally, we have the large 

 intestine (h, i,j, k), separated 

 from the smaller by the 

 ileo-csecal valve, and ter- 

 minating, at its lower ex- 

 tremity, by the anus, at 

 which is situated a double 

 sphincter, for the purpose 

 of guarding its orifice. 

 Everywhere the alimentary 

 canal is composed of a 

 mucous membrane and a 



mUSCular COat, with a layer RCMAS ALIMEXTARY CANAL. n. (Esophagus. 



of submucous areolar tissue IJ^. Bu^T plST L, '' ^ 



between the tWO. The mUS- cendiug colon, t. Transverse colon, j. Descending 

 , . , colon. A-. Rectum. 



cular coat is everywhere 



composed of a double layer of longitudinal and transverse fibres, 

 by the alternate contraction and relaxation of which the food is 

 carried through the canal from above downward. The mucous 



