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HUMAN PHYSIOLOGY 



confuse this with the much smaller glottis, a longitudinal slit opening into 

 the windpipe. Other paired openings are found in the mouth, those lead- 

 ing to the anterior nares or external nostril openings and those leading to 

 the ear, the Eustachian tubes. Make a drawing of the open mouth of a frog, 

 showing these points. 



Buccal Cavity in Man. — In man, the mouth, or buccal cavity, is 

 lined with mucous membrane. Mucous membrane, because it is 

 thinner than the skin, allows the blood to show through, thus 

 giving the characteristic red color of the lips and inner mouth. 

 The roof of the mouth is formed by a plate of bone called the hard 

 palate. This separates the nose cavity from that of the mouth 

 proper. Behind the hard palate the cavities are separated by the 

 soft palate. The part of the mouth cavity back of the soft palate 

 is called the pharynx. From the pharynx lead off the gullet and 

 'Windpipe, the latter placed ventral to the former. The lower part 

 of the buccal cavity is almost filled by a muscular tongue. Ex- 

 amination of its surface with a looking glass shows it to be almost 

 covered in places by tiny projections called papillce. These papil- 

 lae contain organs known as taste hicds, the sensory endings of 

 which determine the taste of substances. The tongue is also 

 used in moving food about in the mouth, in starting it on its way 



to the gullet, while it plays 

 an important part, as we 

 know, in speaking. 



The Teeth. — Plainly the 

 teeth of a frog are not used 

 for cutting or grinding up 

 food; they point inward, 

 a significant fact which 

 shows them to be used for 

 holding. The teeth of man 

 are divided, according to 

 their functions, into four 

 groups. In the center of 

 both the upper and lower jaw in front are found eight teeth with 

 chisel-like edges; these are the incisors, or cutting teeth. Next 

 is found a single tooth on each side (four in all) ; these have rather 

 sharp points; they are the canines; look for them in a cat or dog. 



Teeth; a, incisors; 6, canine; c, premolars; 

 d, molars. 



