FROG. 159 



and the horizontal gape of the mouth extends back beyond the 

 eye. The prominent eyes are perched up on the forehead, and 

 have a fine golden iris and a horizontal pupil. The Frog differs 

 from the Snakes and agrees with the Lizards in having eyelids ; 

 he has also, like the Birds, an additional lid the nictitating 

 membrane. There is a row of delicate teeth along the upper 

 jaw, but none on the lower ; there are others on the palate. 

 The deeply notched tongue is attached by its base to the front 

 part of the mouth, the tip far in towards the throat ; in use it 

 has to be suddenly turned over so that the tip is projected far 

 beyond the muzzle. The large circular depression behind and 

 below the eye is the drum of the Frog's ear. 



The Frog has no neck, the base of his skull coming close to 

 the collar-bones, and there are only a few pairs of very short 

 apologies for ribs between the shoulders and the long pelvis 

 which produces that steep incline at the rear of his back. He 

 is clothed entirely with a smooth, soft skin, which is kept moist 

 by the action of minute mucous glands distributed all over the 

 body. A row of these glands of larger size forms a pale line 

 running back from the eye on either side. The skin plays an 

 important part in the oxygenation of the Frog's blood ; and the 

 experimental physiologists have shown that a Frog deprived of 

 its lungs can carry on its respiration for a lengthened period 

 through the skin alone. Owing to the absence of ribs he has to 

 fill his lungs by swallowing air. 



The male is less portly than the female, and he is further 

 distinguished by having two pads on the first finger which in 

 the breeding season become large rough cushions enabling him 

 to hold his mate. In his throat there is a pair of vocal sacs 

 enabling him to produce his love songs, and when these are in 

 use their inflation causes a distension of the skin of the throat ; 

 but without these adjuncts the female manages to give answering 

 croakings. When these duets are sung under water they produce 

 some curious effects. 



