The luner (Alimentary) Tube and Its Respiratory Derivatives 



27 



of being several or many times longer than the abdominal cavity — a 

 condition necessitating much bending and coiling of the tube. The in- 



Fig. 19. Alimentary canal of frog, 

 Ftana esculenta. (A) Opening of the rec- 

 tum into the cloaca (CI); (D) ileum; (Du) 

 duodenum; (f) boundary between small 

 and large intestine; (HB) urinary bladder; 

 (M) stomach; (Mz) spleen; (Oe) esopha- 

 gus; (Py) pyloric region; (Ft) rectum. 

 (From Wiedersheim : " Comparative Anat- 

 omy of Vertebrates." By permission of 

 The Macmillan Company, publishers.) 



ternal surface is complicated by inwardly projecting folds consisting of 

 the digestive (or "mucous") epithelium and its underlying con- 

 nective tissue submucosa. Such folds form the prominent ridges or 



