EXTERNAL CHARAOTBES. 13 



Discoglossidse (Fig. 3, a) ; circular and entire or 

 feebly nicked behind in the Pelohatidse and Hyla 

 (Fig. 3, o), resembling a mushroom when thrust out; 

 elliptical or pyriform and entire in Bufo (Fig. 3, b) ; 

 oval and forked behind in Bana (Fig. 3, d). In the 

 two latter genera the extensibility of the tongue is so 

 great that a large specimen is able to seize a prey two 

 inches distant from it. 



Owing to the nature of the skin and the absence of 

 true ribs, the shape of the body varies enormously 

 according to the degree of moisture of the sub- 

 cutaneous sacs, the inflation of the lungs, or the 

 condition of the ovaries, and all measurements that 

 are not based on the bony framework are useless for 

 systematic purposes. The frogs of the genus Rana 

 appear hump-backed in a squatting posture, an angle 

 being produced at the articulation of the cylindrical 

 sacral diapophyses with the ilia; the other genera, 

 with flattened and dilated sacral diapophyses, have a 

 rounded back when at rest, as may be seen on com- 

 paring a true frog with a toad or tree-frog. The 

 vent, or cloacal opening, is a small rounded orifice at 

 the very posterior extremity of the body, above and 

 between the thighs. 



The fore limb is divided into a hradimm or arm, an 

 antebrachmm or forearm, and a manus or hand with 

 four functional fingers, of which the third is the 

 longest. The length of the first finger as compared 

 to the second is often used as a specific character. 

 In order to preclude misunderstandings, it is well to 

 remark that when the first finger is stated to extend 

 as far as or beyond the second, the two are taken to 

 meet halfway. A rudimentary pollex is often indicated 

 externally by a tubercle at the base of the inner finger 

 (Fig. 4, a). 



The hind limb is longer, usually very much longer, 

 than the fore limb, and divided into four distinct 

 segments — the femur or thigh, the cms or tibia, or 

 leg, the tarsus, and the pes or foot. Anatomically, 



