THE DIGESTIVE SYSTEM 



The digestive system consists of the mouth cavity, 

 pharynx, esophagus, stomach, small and large intestines, 

 salivary glands, liver and pancreas. 



The mouth opening is triangular. It is located on the 

 anteroventral surface of the head some distance back from 

 the tip of the snout. The lower lip conceals the greater 

 part of the two long lower incisor teeth. Externally it is 

 hairy; internally it is covered with smooth mucous mem- 

 brane. A fleshy ridge on its inner surface fits into the 

 space between the incisor teeth. This ridge joins ventrally 

 a short vertical septum, the frenulum, which passes between 

 the incisor teeth, connecting the lip with the mandible. 

 From the angle of the mouth a lobe of integument, covered 

 with hair, turns upward along the inner surface of the 

 cheek. 



The lateral halves of the upper lip meet in front at an 

 acute angle pointed toward the nasal septum. The apex 

 of the angle is connected with the septum by a groove. The 

 upper lip is therefore cleft, exposing the incisor teeth of 

 the upper jaw. A frenulum is lacking. The edge of each 

 upper lip immediately behind the incisor teeth is turned 

 inward, forming a lobe whose lower hairy surface touches 

 the dorsal surface of the tongue. This lobe is hairless dor- 

 sally, and is in contact here with the roof of the mouth. 

 The lip lobes, tongue, and a fleshy tubercle on the mid- 

 dorsal surface of the mouth's roof just behind the lobes, 

 are all in contact with one another when the jaw is closed, 

 practically separating the mouth opening from the mouth 

 cavity. 



