14 INTEODUCTION. 



the tarsus is, of course, part of the foot proper ; but 

 as it hei'e forms a distinct segment, the term foot is 

 used in a restricted sense. The foot is measured from 

 the base of the metatarsal tubercle ; it has five elon- 

 gate toes, gradually increasing in length to the 

 fourth, the fifth being again shoi'ter. There is in 

 addition a rudimentary sixth toe, the so-called prse- 

 hallux, conspicuous externally in the form of a 

 tubercle or spur at the base of the inner toe. In 

 Pelobates (Fig. 4, b) this preehallux or inner metatarsal 

 tubercle acquires a very great development, is covered 

 by a horny sheath with sharp cutting edge, and serves 

 as a shovel for digging in the soil. There is often 

 another tubercle on the sole, at the base of the 

 fourth toe ; this so-called outer metatarsal tubercle 

 (Fig. 4, o) is merely a thickening of the integument. 



Fig. 4. 



A. Tia,n<i ol Alytes obstetricans. b. Foot ol Pelobates fiiscus. c. Foot 

 oi Bufo calamita (lower views). 



Other dermal tubercles are usually present, more or less 

 developed, single (Fig. 6, a, p. 16) or paired (Fig. 4, c), 

 under the digits at the articulations between the 

 phalanges; they are called subarticular tubercles. 

 The fingers are free except in Hyla arhorea, in which 

 they are provided with a rudimentary web. The toes 

 are more or less webbed or bordered by membranes in 

 all our Batrachians, but the extent of the web varies 

 greatly according to the species, and is usually more 

 developed in males than in females, especially during 

 the breeding season. The web is usually smooth and 

 transparent ; it is thicker, and often warty, especially 

 towards the margin, in Bufo. 



