188 THE ANATOMY OF TEETEBRATED ANIMALS. 



snake-like Gymnophiona, the right is mucli smaller than the 

 left. In Proteus, the imlmonary blood is not all returned 

 to the heart, some of it entering the veins of the tnink. 

 Aerial respiration is effected, in the Amphibia, by pumping 

 the air from the oral cavity into the lungs. To this end 

 the mouth is kept shut, and ingress and egress to the air is 

 given by the nasal passages, which always open immediately 

 behind the vomers, at the anterior part of the roof of 

 the mouth. These passages being open, and the hyoidean 



Fig. .59. 



. p». 



S.rk. 



Fig 59. — The brain of liana esculentn, from above, magnified four 

 times:— L. ol., the rhinencephalon, or olfactory lobes, with, I., the 

 olfactory nerves ; He, the cerebral hemispheres ; Fk. o., the thala- 

 mencephalon with the pineal gland, Pn. ; L. op., optic lobes ; C, 

 cerebellum; S. rh., the fourth ventricle; Mo., medulla oblongata. 



ai^paratns depressed, the air fills the cavity of the mouth. 

 The external nostrils are then shut, and the hyoidean appa- 

 ratus being raised, the air is forced, through the open glottis, 

 into the lungs. 



All Amphibia possess an urinary bladder, which opens into 

 the cloaca, and does not receive the iireters. The kidneys of 

 the Amphibia appear, like those of fishes, to be persistent 

 Wolf&an bodies. 



