304 THE VIVARIUM. 
(3) There are small teeth on the inner margins of the upper 
jaws, but none at all on the lower ones. There are also some 
little teeth towards the front of the palate known as vomerine teeth. 
(4) The skin of the Frog is naked and moist. 
(5) The tongue of this animal is a very curious contrivance, 
being, unlike most other tongues, fixed in front and free behind. 
The Frog captures its prey by throwing forward, beyond the ex- 
tremity of the mouth, the free hinder portion of tongue, which 
being covered with sticky secretion attaches itself to the victim 
and withdraws it into the mouth. 
(6) The Frog, possessing no ribs to help in respiration, 
depends, in this matter, upon the assistance of its tongue, which 
it uses in the following manner, as described by Mr. St. George 
Mivart: ‘‘ The mouth is filled with air through the nostrils and 
kept shut, while the internal openings of the nostrils are stopped 
by the tongue, and the entrance to the gullet is closed. Then by 
the contraction of the muscles attached to it, the os-hyoides is 
elevated, and every other exit from the mouth being closed, 
except that leading to the larynx, air is thus driven down the 
glottis into the lungs.” Thus for pulmonary respiration it is 
necessary to the Frog to keep the mouth shut; and in this way, 
but for the action of the skin, the animal might be choked by 
keeping the mouth open. The external movements which the 
Frog makes as it thus pumps the air into the lungs are very 
manifest and frequent. 
(7) Owing to the fact that all Reptiles and Batrachians, except 
the Crocodilia (and their blood, too, is mixed just outside the 
heart), have only three complete chambers in the heart (two 
auricles and one ventricle), and not four, as in warm-blooded 
animals, the oxygenated, or fresh blood, and the unoxygenated, 
or effete blood, become mingled in the one ventricle. But in the 
case of the Frog, because of an extraordinary arrangement by 
which the skin is made to assist in the work of respiration, ‘‘ the 
unoxygenated fluid from the body is sent to the purifying respira- 
tory surfaces (lungs and skin), and the pure, oxygenated blood 
alone goes to the head and the brain.”’ 
One of the experiments which tended to prove the existence of 
cutaneous respiration in the Frog was the tying of a piece of 
