RANA. 339 
and other small animals, but retires through the day into 
water or rocky holes. In the winter the frog hibernates in 
pond-mud or in holes. 
The Head is set upon the ¢runhk with no neck and the 
latter carries two conspicuous pairs of limbs. ‘The mouth, 
when open, is a wide gaping fissure, literally 
extending ‘‘from ear to ear.” At the tip of the 
“nose” is a pair of small external nares leading 
into the olfactory or nasal sacs. Further back are the eyes, 
and a little behind and below them are the tympanic mem- 
branes of the ears or auditory organs. These are covered 
with skin and appear as round surfaces. The front limbs 
have four digits, the thumb being absent. The ind limbs 
have five long toes or digits with a web stretched between 
them. The male Rana temporaria in the breeding season 
has a thickened callosity on the first digit of each fore-limb. 
Dorsal to the junction of the hind limbs and the trunk is a 
single cloacal aperture. 
The whole body is enclothed in a loose moist skin, with 
an entire absence of scales, hairs, or other exoskeleton. 
There are abundant skin-glands’ which serve 
to keep the skin moist. Under the skin are 
numerous blood-vessels which enable the skin 
to assist in the function of respiration. 
The skin has scattered pigment of various colours, and 
the frog has the power to adapt its general coloration to its 
surroundings fairly rapidly. If the jaws be widely opened 
the duccal cavity is exposed. The fongue is forked, free 
behind and fastened at the front end; it can be shot out 
with great rapidity for catching insects.*' The lower jaw has 
no teeth, but a row of delicate teeth lines the upper. In 
addition there-are in the roof of the mouth two patches of 
small vomerine teeth, so-called because they are on the 
vomer bones. ; 
Just behind these teeth are paired zzdernal nares leading 
to the exterior by the nasal sacs and the external nares. 
They serve for the introduction of air. Further back, near 
the angles of the jaw, is found on each side a widely-open 
passage, the Eustachian tube, leading almost at once into the 
External 
Features. 
Integu- 
mentary. 
* The tongue is protruded by the pressure of lymph forced into its interior by the 
contraction of muscles, such as the mylohyoid. 
