102 THE ANATOMY OF VERTEBRATED ANIMALS. 



state, are either external branchise, combined with lungs, a3 

 in the perennibranchiate Urodela ; or lungs only, as in the 

 other Urodela, the Batraehia, the Gymnophiona, and, prob- 

 ably, the majority of the Lahyrinthodonta. 



In the perennibranchiate Urodela, the branchial arches (or 

 some of them) are separated by open clefts (the number of 

 which varies from four to two), throughout life, and three, 

 branched, gills are continued by single stems into the integu- 

 ment, at the dorsal ends of the branchial arches. An opercular 

 fold of the integument, in front of the gill-clefts, attains a 

 considerable size in Siredon (Fig. 58), but does not cover the 

 gills. The branchial arches themselves bear no branchial fila- 

 ments. Other Urodela are devoid of external gills, but (as is 

 the case in Menopoma and Amphiuma) present one or two 

 small gill-clefts on each side of the neck, and are thence called 

 Derotremata. The rest of the Urodela, and all the Hatrachia 

 and Gymnophiona, are devoid of both external gills and gill- 

 clells, in tlie adult state. 



In all the Amphibia, a glottis, placed on 

 the ventral wall of the oesophag-us, opens into a 

 sliort laryngo-tracheal chamber with which two 

 pulmonary sacs are connected, either directly, 

 or by the intermediation of bronchi (as in the 

 Aglossa), or by a trachea (as in the Gymno- 

 phiona). The walls of the pulmonary sacs 

 'are more or less sacculated. In most Am- 

 phibia the lungs are equal in size ; but in the 

 snake-like Gymnophiona, the right is much 

 smaller than the left. In Proteus, the pul- 

 monary blood is not all returned to the heart, 

 some of it entering the veins of the trunk. 

 Aerial respiration is effected, in the Amphibia, 

 by pumping the air from the oral cavity into 

 -The brain of the luiis's. To this end the mouth is kept 



Jiana CHCulenta, i.i. t ,,-,... ^ 



from, above, magni- Shut, and mgress and egress to the air is given 

 toe'itat^epMOTt'by the nasal passages, which always open 

 or olfactory lobes, immediately behind the vomers, at the anterior 

 tory' nerves; /fo., P'i-rt of the roofof the mouth. These passages 

 the cerebral hemi- being opcu, and the hyoidcan apparatus de- 

 ihaianiencepiiaion pressed, the air fills the cavity of the mouth. 

 ^land, p'l: l^^t, '^'^® external nostrils are then shut, and, the 

 optic lobes; c, cere- hyoidean apparatus being raised, the air is 

 fou "til ventricle; forccd, through the open glottis, into the lungs, 

 Mo^ medulla i.bion- ^\ Amphibia posscss a urinary bladder, 



