4 o6 MANUAL OF ZOOLOGY SECT. 



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 (see 



FIG. 230. Rana temporaria. (From Mivart.) 



p. 408). 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 backwards and down- 

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

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

 four short tapering digits, directed forwards. The hind- 

 limb is of great size ; in the usual squatting posture the 



