EXTERNAL CHARAOTEES. 11 



pupil appears nearly round, or straight when the 

 subtriangular form obtains (Fig. 2, a). In some 

 specimens of Bomhinator the upper border is even 

 emarginate, so as to produce the shape of a heart ; and 

 when extremely contracted the pupil divides into 

 three branches, aflPecting the shape of a Y (Fig. 2, a) 

 This type of pupil approaches the vertical, and in 

 some specimens of Discoglossus the much-contracted 

 pupil is in fact a little deeper than broad. In Alytes, 

 Pelodijtes, and Pelohates (Fig. 2, b, c) we find a regular 

 cat's pupil, vertically elliptical or club-shaped, linear 

 when fully contracted. 



The tympanum, or drum of the ear, is absent in 

 Bomhinator and Pelohates. When present it may be 

 concealed under the skin, as in some specimens of 

 Discoglossus, Pelodytes', and Bufo viilgaris, or appear 

 on the temple behind the eye as a round or oval disk 

 covered with tbin skin (Fig. 1, a, p. 9). 



The mouth is large, and cleft to beyond the eyes. 

 The jaws are edentulous in Bufo ; the upper is armed 

 with numerous closely-set teeth in the other genera — 

 ten to fifteen in each pr^maxillary, forty to fifty in 

 each maxillary. The teeth have sharply-pointed, 

 slightly-hooked crowns with long shafts applied to 

 the inner side of the pr ^maxillary and maxillary 

 bones. The palate (Fig. 3, p. 12) is pierced by two 

 pairs of orifices, the choanas, or inner openings of the 

 nostrils anteriorly, and the openings of the Eusta- 

 chian or auditory tubes, situated near the commis- 

 sures of the jaws; the Eustachian tubes are extremely 

 fine, or sometimes even indistinct, in Bomhinator. In 

 all the genera except Bufo there are two groups or 

 series of teeth, each implanted on an eminence of the 

 vomerine bones ; these vomerine teeth are situated 

 between or behind the choanas, as shown on p. 12, 

 Fig. 3, A, c, D. 



The tongue, thick and papillose, flat, is attached in 

 front and in the middle, and the posterior portion, by 

 being bent over and rapidly thrust out of the mouth, 



