564 TEXTBOOK OF ZOOLOGY 



another by a vertical partition supported by the vomerine bones of 

 the skull. The Eustachian pits are paired diverticula from the dorsal 

 wall of the pharynx continuous with the tympanic cavities, which 

 are closed externally by the tympanic memtranes. The mouth cavity 

 ends posteriorly as the pharyngeal cavity which is produced poste- 

 riorly into the horizontal slit which leads to the esophagus. The 

 glottis, or aperture of the trachea, is located centrally on the summit 

 of the laryngeal chamher. The tongue is a fleshy organ lying on the 

 floor of the mouth. It is furnished with many tactile and gustatory 

 cells, and is usuallj^ covered with a sticky secretion which assists it 

 in catching and holding prey. It can be extended from the mouth 

 and is used in capturing insects. 



The tubular esophagus opens into the mouth cavity by way of a 

 horizontal slit posterior to the pharjmgeal cavity. It is deeply pig- 

 mented anteriorly and lies dorsal to the trachea. The walls are thick 

 and muscular. It opens posteriorly into the cardiac portion of the 

 stomach. 



The stomach is a cylindrical, muscular organ with relatively thick 

 walls. When empty it is but little greater in diameter than the 

 esophagus or the intestine. Since it lies chiefly on the left side of 

 the body, it is largely concealed by the left lobe of the liver. It is 

 larger at the anterior or cardiac end and constricted at the posterior 

 or pyloric end. The pyloric valve is an annular ridge of muscular 

 tissue which narrows or closes the aperture between the stomach and 

 the small intestine. The inner surface of the walls of the stomach 

 is thrown into longitudinal folds or rugae. Distributed over the 

 entire inner surface are the openings of minute ducts from the numer- 

 ous gastric glands which secrete the gastric juice. This digestive fluid 

 normally begins the digestion of proteins in the food. 



The intestine forms several coils in the posterior third of the coelom, 

 and is held in place by the mesenteries. As is commonly the case 

 in insectivorous or carnivorous animals the intestine is relatively short. 

 The anterior part of the small intestine is the duodenum. The com- 

 mon bile duct from the liver and the pancreatic duct from the pan- 

 creas join this section of the intestine. There is no definite division 

 between the duodenum and the ileum, the succeeding portion of the 

 intestine. After several turns the ileum passes into the large intestine 

 on the right side of the body. An annular ridge of tissue, the ilea- 



