VOICE. 61 



VIII. Voice. 



All our male Batrachiaiis are endowed with a voice, 

 which they produce at least dmnng the pairing season. 

 Females are mute, or respond to the male by a mere 

 grunt. The larynx is provided with vocal cords, 

 which are set vibrating as the air is rapidly shifted 

 from the lungs into the buccal cavity. In many 

 species the sound is intensified by resonance in 

 special vocal sacs situated in the gular region, or at 

 the sides of the head behind the commissures of the 

 jaws. The vocal sacs are called internal when 



Fig. 23. 



-< K Y > 



A B 



A. Bana esculenta, ^, with inflated external vocal sacs (lower view). 



B. Rano, temporaria, ^, witli inflated internal vocal sacs (lower view). 



covered by the unmodified gular integument, how- 

 ever much this may be distended ; external when their 

 membrane, a diverticulum of the mylohyoid muscle, 

 projects through slits at the sides of the throat, as 

 in Rana esculenta, or when the skin is thinned and 

 converted into a bladder-like pouch, as in Hyla 

 arborea. In some forms there are two distinct 

 sacs, in others but one. The air penetrates by one or 

 two openings in the floor of the mouth, small, rounded, 

 and situated near the commissures of the jaws, as 



