EXTERNAL CHARACTERS. 9 



II. External Characters. 



As these Batrachians have no neck, the head passes 

 directly into the body, and, except in Pelobates, where 

 the skin is closely adherent to the rugose skull, the 

 demarcation is consequently difficult to trace. By 

 drawing a line connecting the articular extremities 

 of the mandible we obtain approximately the exact 

 length of the head, the greatest width being at the 

 commissures of the jaws. The head is more or less 

 flattened, with prominent eyeballs covered above by 

 the upper eyelid, which is continuous with the rest of 

 the cephalic integument. The upper surface of the 

 head may be limited on each side by an angular line 

 extending from the tip of the snout to the upper 



Fig. 1. 



Upper views of heads of (a) Rami temporaria and 

 (b) Bombinator igneus. 



eyelid, the cantkus rostralis, continued behind as a 

 ridge or fold, the supra-temporal ridge (Fig. 1, a). 

 In some forms, such as Bombinator igneus (Fig. 1, b), 

 the snout is simply arched from one lip to the other, 

 and there is no trace of a canthus rostralis. The side 

 of the snout below the canthus rostralis is called the 

 loreal rep;ion. The lenp-th of the snout is taken bv 

 applying the points of the compasses to the anterior 

 border of the (bony) orbit and the very tip of the 

 snout, on the median line. 



The nostrils are small valvular openings, situated 

 between the end of the snout and the eves, alter- 



