THE ORAL CAVITY 



An etherized frog is best adapted to this study. Note that the 

 jaws fit together very tightly. Open the mouth to its full 

 extent and note the wide mouth (oral) cavity the posterior por- 

 tion of which, the pharynx, is continued caudad into the eso- 

 phagus. In the roof of the mouth identify the structures men- 

 tioned in the paragraphs which follow. 



There are two groups of teeth found in this animal. The 

 maxillary teeth form a row about the edge of the upper jaw 

 where they are borne by the maxillary and premaxillary bones. 

 The vomerine teeth form two small patches in the cephalic part 

 of the roof of the mouth and near the middle line. They are 

 attached to the vomers (vomerine bones). 



Locate again the posterior nares lying laterad of the two groups 

 of vomerine teeth. The eustachian tubes open into the oral cavity 

 through large apertures at the sides of the posterior part of the 

 mouth cavity. Each tube enters a shghtly dilated chamber, 

 the tympanic cavity (or middle ear), which lodges the columella 

 and is closed externally by the tympanic membrane already 

 seen in the study of the surface of the head. Pass a beaded 

 bristle through the opening of one of the eustachian tubes and 

 determine the results. If necessary make a slit in the tympanum. 



Two rounded prominences on the sides of the roof of the mouth 

 are caused by the eyeballs. Press down upon one of the eyes with 

 the finger and note results. 



The floor of the mouth cavity presents several features to be 

 noted. The lower jaw, which lacks teeth, forms a bony margin 

 for the floor of the mouth. The greater extent of the floor 

 is soft and supported by a cartilaginous plate, the body of 

 the hyoid. The tongue is attached to the cephalic portion of 

 the floor and has its free bilobed end turned caudad toward the 

 esophagus. If this organ is drawn cephalad the structures 

 about to be described may be seen more readily. 



The glottis, or aperture leading into the lungs, is a longitudinal 

 slit upon the apex of a prominence, just cephalad of the eso- 

 phagus. It is supported laterally by the arytenoid cartilages 



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