2O THE FROG 



(/) In the male: the openings of the vocal sacs just 

 within the angle of the mouth. 



The posterior part of the mouth cavity, into which the 

 glottis and the Eustachian tubes open, is called the pharynx. 



Sketch the floor and the roof of the mouth, twice natural 

 size, labeling all the parts. 



B. Ciliated epithelium is found lining the oesophagus 

 and the roof of the mouth of the frog, and may be demon- 

 strated as follows : Gently scrape the roof of the mouth of a 

 recently-killed frog, transfer the scrapings to a slide and 

 mount in mucus from the frog's mouth or in normal salt 

 solution. Examine with the high power of the microscope. 

 At the free edges of some of the cells a shimmering move- 

 ment will be seen; this is often so rapid that it is impossible 

 to see the cilia which cause it, but after the movement has 

 slackened somewhat it can be seen to be due to delicate, hair- 

 like processes of the cells. The stroke of a cilium is always 

 stronger in one direction and all the cilia beat in the same 

 direction. Draw some of the cells and their cilia. 



An excellent example of ciliated epithelium is afforded 

 by the gills of the fresh-water mussel; mount a small piece 

 (a single layer) of the gill in water. 



The following demonstration will be prepared by an in- 

 structor: Place a recently-killed frog on its back, cut away 

 the lower jaw and the floor of the mouth in order to ex- 

 pose the roof of the mouth, and place' some powdered car- 

 mine or bits of cork on the roof of the mouth. Observe that 

 the particles are carried slowly back toward the oesophagus ; 

 how? 



