228 THE BIOLOGY OF THE ANIMAL 



nares? To the vomerine teeth? "What is their 

 shape ? Pass a bristle through from the external 

 openings. 



Look back, near the union of the two jaws, 

 and find 



c. The openings of the Eustachian tubes. — 



What is their exact position ? How do they com- 

 pare in size with the posterior nares? Pass a 

 bristle into one of the openings, then remove the 

 tympanic membrane of the same side. Into what 

 cavity does the Eustachian tube lead ? 



Make a sketch of the roof of the mouth. Ex- 

 amine the floor of the mouth. 



Do you find that any part of the floor is firmer 

 than the rest? If so, where is this part, and to 

 what is the firmness due ? 



d. The tongue. — Does it entirely cover the floor of 

 the mouth ? What is its shape ? Size ? Where 

 is it attached? Can the tip of the tongue be 

 thrust out of the mouth ? What is the character 

 of the upper surface of the tongue ? Xote the 

 papillae covering this surface. Compare the 

 lower with the upper surface. What reasons 

 can you give for the shape of the posterior end ? 



Back of the tongue find an opening, 



e. The glottis. — What is its shape? What is the 

 nature of its margin? What is the arrangement 

 of the mucous membrane on each side of the 

 glottis ? 



Pass a stiff guarded bristle back of the glot- 

 tis, and note that it passes into another opening, 

 which leads into the oesophagus. 



