16 GENERAL ANATOMY OF THE FROG 



3. The skin is moist and smooth ; and devoid of hairs, scales, 

 and claws. The colour of the skin is variable in different 

 specimens and at different times : it is mottled on the dorsal 

 surface, paler on the ventral. 



4. The head is flat and triangular, with a blunt apex directed 

 forwards. 



At the sides of the head are the eyes, which are large and 

 prominent. Each eye has two eyelids, of which the upper is 

 thick, pigmented, and almost immovable, while the lower is 

 semi-transparent and freely movable. 



Behind the eye on either side is an obliquely placed elongated 

 patch of a dark colour, in the middle of which is a circular 

 area the tympanic membrane supported by a firm marginal 

 ring. 



5. The limbs. There are two pairs of limbs, fore and hind ; 

 each limb being composed of three segments. 



a. The Fore limb presents the following divisions : 



i. Arm. 

 ii. Forearm. 



iii. Hand, with four digits, corresponding to the four 

 fingers of man ; the thumb being very small and 

 inconspicuous. In the male frog there is a pig- 

 mented thickening along the inner edge of the first 

 digit, specially developed at the breeding season. 



b. The Hind limb is much longer than the fore limb, and 



divided into the following parts : 

 i. Thigh, 

 ii. Leg. 

 iii. Foot, with five toes webbed together. The shortest 



toe corresponds to the big toe of man, and the 



longest to his fourth toe. 



6. External apertures : or openings on the surface of the 

 body. 



a. Median apertures. 



i. The Mouth is a wide horizontal slit. 

 ii. The Cloacal aperture is a small hole at the posterior 

 end of the body, between the legs : it lies slightly 

 on the dorsal surface, just behind the bony projec- 

 tion formed by the posterior end of the urostyle. 



