xni PHYLUM CHORDATA 2<J5 



in America ; JR. esculentci is the large green edible Frog found on the 

 continent of Europe and occasionally in England ; R. pipiens is the 

 commonest North American species of the genus. Other species 

 of the same genus occur in all parts of the world except New 

 Zealand, the southern part of South America, and the various 

 oceanic islands. 



External Characters. The trunk is short and stout, and is 

 continued, without the intermediation of a neck, into the broad, 

 depressed head. There is no trace of a tail, the anus being terminal. 

 The mouth also is terminal, and is characterised by its extra- 

 ordinary width, the gape extending considerably behind the eye. 

 On the dorsal surface of the snout are the small nostrils ; the eyes 



FIG. 921. Rana temporaria. (From Mivart.) 



are large and prominent, and each is provided with an upper eyelid 

 in the form of a thick fold of skin, and a nictitating membrane, a 

 much thinner fold, which arises from the lower margin of the eye 

 and can be drawn up over it. Close behind the eye is a circular 

 area of tensely-stretched skin, the tympanic membrane, a structure 

 not met with in any Fish : as we shall see, it is an accessory 

 part of the auditory organ. There is no trace of branchial 

 apertures. 



The back has a peculiar bend or hump, in the sitting posture, 

 marking the position of the sacral vertebra. The limbs are of 

 very unequal size. The fore-limbs are short, and each consists of 

 an upper arm, which, in the ordinary position, is directed back- 

 wards and downwards from the shoulder-joint; a, fore-arm, directed 

 downwards and forwards from the elbow ; and a hand, ending in 



