198 THE BIOLOGY OF THE ANIMAL 



. Internal Anatomy. 

 A. — The Digestive System. 



Using an alcoholic specimen, push a guarded 

 bristle into the mouth, and with scissors cut open 

 the alimentary canal from the mouth to the 

 stomach, using the bristle as a guide. Then in a 

 similar manner trace the course of the intestine 

 backwards from the anus. If necessary, the ali- 

 mentary canal may be injected through the anus 

 with a mixture of equal parts of plaster of Paris 

 and water. The mixture must be strained through 

 fine cloth before being used. 



a. The mouth. — This has already been studied. 



i. The oesophagus — What is its relation to the 

 mouth as regards diameter and the direction in 

 which it runs ? To the anterior adductor muscle ? 

 What is the nature of its walls ? 



c. The stomach. — How is it distinguished from the 



oesophagus ? What is its position with regard to 

 the hinge-ligament ? 



Find surrounding the stomach and cesophagus 

 a dark-colored mass, 



d. The liver. — What is its relation to the anterior 



adductor muscle ? Look for the opening of the 

 bile-duct into the cesophagus anterior to the 

 opening of the latter into the stomach, and into 

 the stomach itself. 



e. The intestine. — Into what part of the stomach 



does it open? Trace it through the yellowish- 

 white generative gland, by picking away the 

 latter with the fine forceps. Does it enter the sub- 

 stance of the foot? What is its course through 



