8 INTRODUCTION. 



width) : the fronto-parietal bones are wide and flat. The tympanic 

 membrane, in comparison with the eye, is smaller than in R. esculenta, 

 and is usually less distinguishable from the surrounding- parts as 

 regards colour and transparency. The apertures of the Eustachian 

 tubes are, relatively to the posterior nares, larger than in the water- 

 frog. The vomerine teeth are comparatively small and lie in two 

 groups placed obliquely to each other, their anterior ends diverging 

 from each other and being prolonged as ridges to the anterior 

 margins of the posterior nares. The two groups do not lie between 



Fig. 2. 



The brown grass-frog, liana temporaria, L. 



the nasal apertures, but behind a line drawn transversely through 

 their posterior margins. Vocal sacs are absent in both sexes. 

 The hind legs are relatively shorter : the toes are not so evenly 

 tapered off, indeed they are slightly swollen : the fourth toe, 

 as compared with the third and fifth, is somewhat longer than in 

 R. esculenta the web of this toe does not extend to the tip of the 

 toe, but terminates in both sexes at the last phalanx but one ; the 

 web on the third toe is less developed on the thumb side than 

 on the other : on the remaining toes also the margins of the web 



