70 THE BIOLOGY OF THE FROG chap. 



nuity with these organs may be shown by passing a bristle 

 into them or by inflating them by means of a blowpipe. 

 Posteriorly the buccal cavity presents two openings in the 

 middle line. The ventral opening, or glottis, is a narrow 

 longitudinal slit in the middle of a prominence caused by 

 the cartilages and muscles of the larynx ; it is kept closed 

 except during the passage of air into or out of the lungs. 

 The dorsal opening marks the beginning of the esophagus, 

 which leads to the stomach. Although capable of great 

 distention, the esophagus is kept closed except when food 

 is being swallowed. 



The floor of the mouth is very distensible and undergoes 

 continuous movement in respiration. In the middle part 

 may be seen the hyoid cartilage, which gives attachment for 

 the tongue and several muscles that move the floor of the 

 mouth. The tongue of the frog is attached in front to 

 the lower jaw and below to the hyoid cartilage. Its shape is 

 subject to great variation according to the degree of con- 

 traction of its various muscles, but in its normal relaxed 

 condition it is oblong, flattened, somewhat narrowed in 

 front, and produced at its posterior angles into two lobes 

 which extend backward on either side of the glottis ; the 

 posterior margin is concave, and the sides, which project over 

 the attachment at the base, leave a considerable space of the 

 floor of the mouth uncovered. In the mucous membrane 

 covering the tongue there are numerous glands which secrete 

 the mucus by which this organ is always covered. There is 

 also a large number of papillae, of which there are two kinds : 

 the filiform, which are conical or threadlike in shape, and 

 the fungiform, which are larger and less numerous than the 

 former. The latter are narrow at the base and expanded at 

 the distal end. In an average specimen of R.fusca Fixsen 

 found two hundred and thirty-eight of these papillae. In a 



