BUCCAL CAVITY AND RESPIRATORY ORGANS 1 



1. Pin the Frog which you previously dissected, ventral surface up, in a 

 dissecting pan. Pull back the lower jaw, cutting a little at each corner, and 

 then pin the edge of the lower jaw to the ventral surface of the body so as 

 to expose fully the cavity of the mouth (buccal cavity). 



2. Note the upper jaw with (a) a projecting, fleshy upper lip, and 

 bearing (b) numerous very fine maxillary teeth, which you can feel by 

 rubbing over them with your finger ; (c) the two groups of vomerine 

 teeth on the dorsal roof of the mouth ; (d) the olfactory openings (in- 

 ternal nares), one on either side of the vomerine teeth ; (e) the openings 

 of the eustachian tubes, posterior to the internal nares. 



3. Note the lower jaw with (a) the muscular tongue, which is attached 

 anteriorly, and (b) the circular elevation with a median, slit-like opening 

 (glottis) into the tracheal cavity which leads to the lungs. Leading 

 from the posterior end of the mouth is (c) the esophagus which con- 

 tinues to the stomach. Make a drawing of the entire mouth cavity to 

 show the structures observed. 



4. Place the lower jaw in a normal position and then carefully remove 

 the skin from the ventral surface of the body, anterior to the fore limbs. 

 Carefully cut the connecting blood vessels, and remove the heart from the 

 body. Locate the lungs which you saw in a previous exercise and trace 

 each one to the thin walled tracheal cavity which lies just ventral to the 

 glottis, as noted in paragraph 3. Now remove the lungs, tracheal cavity, 

 and glottis, after having carefully cut around the glottis with the scissors, 

 and pin them out in a dissecting pan. With fine 'scissors, make a median 

 longitudinal cut through the ventral wall of each lung and continue each 

 cut into the tracheal cavity. Pin back the cut surfaces so as to expose the 

 interior of the various structures. Note : (a) the structure of the lungs ; 

 (6) the structure of the tracheal cavity, with (c) the pair of vocal cords 

 lying on each side. Draw to show the structure as observed. 



5. Study a model of a median longitudinal section of a human head and 

 neck, showing the mouth, or buccal cavity, and the throat cavity, or 

 pharynx. Note that the mouth cavity is bounded dorsally by (a) a 

 bony partition (hard palate) which separates it from (6) the nasal 

 cavity above. The hard palate extends posteriorly and merges into 

 (c) the soft palate which partially separates the mouth cavity from the 

 pharynx. On each side the mouth cavity is enclosed by the cheeks and 

 by the jaws bearing teeth. Below, the mouth cavity is bounded by (d) the 

 thick muscular tongue. Note further that both the nasal cavity and the 

 buccal cavity open into the pharynx through which both the food and the 

 air pass. Then the trachea, protected by the epiglottis, branches off to 

 the lungs, and the esophagus continues to the stomach. (W. f. 109.) 



1 B. pp. 189-192. 

 329 



