14 GENERAL ANATOMY OP THE FROG. 



3. The skin is moist and smooth ; and devoid of liairs, 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 immoveable, while the lower is 

 semi-transparent and freely moveable. 



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 tw^o 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 thicken- 

 ing along the inner edge of the first digit, specially 

 developed at the breeding season. 



1). 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 pro- 

 jection formed by the posterior end of the urostyle. 



