180 VERTEBRATES. 



5. The mucilaginous saliva which covers the tongue. 

 When a fly, or other insect suitable for food, comes near 

 enough, the frog darts out this sticky tongue, and draws 

 the entangled fly into its mouth. 



Pass a bristle into the nostrils from the outside, and 

 discover where they open into the mouth. 



Cut a hole in the tympanic membrane, and insert a 

 bristle into the cavity it covers, and push the bristle into 

 the mouth. The wide tube by which it enters the mouth 

 is the Eustachian tube. 



The posterior, funnel-shaped part of the cavity seen on 

 looking into the mouth is the pharynx. Its folded walls 

 converge toward the esophagus. 



On the floor of the pharynx is a narrow slit which 

 leads into the trachea, and thence to the lungs. Pass a 

 bristle into this slit. 



Find a small, isolated patch of teeth on the roof of the 

 mouth. 



Dissection. Dissect the frog under water. A pre- 

 pared skeleton should be at hand for reference in locating 

 bony parts. 



Cut through the skin along the median ventral line, 

 from the mandible to the posterior end of the body. 

 Make a second cut at right angles to the first, entirely 

 across the middle of the ventral surface, and turn back 

 the four flaps of skin thus formed. This will expose the 

 thin, muscular abdominal wall. Observe a dark vein 

 showing through the abdominal muscle on the median 

 line. Make a longitudinal cut through the body wall, 

 a little to one side of the median line, so as to avoid 

 injuring this vein, and continue the cut forward to the 

 bony pectoral arch, or shoulder girdle. Then consult a 

 skeleton, to see how, by cutting to one side of the median 

 line, you may avoid injuring the elongated median bone 



