378 



COMPARATIVE ANATOMY 



of trabecula?, forming a system of alveoli lining the vesicles 

 (Fig. 284). The lungs are, as a rule, equal in size ; in form they 

 are cylindrical in Salamanders, and elliptical in Anurans. In the 

 long-bodied Gymnophiona the right lung alone is fully developed, 

 the left being only a few millimetres long. 



The mechanism of respiration is briefly as follows. The floor of 

 the mouth (which is kept closed) is lowered, and thus air is 

 inspired through the nostrils, which are then closed by a special 

 mechanism, while the glottis is pressed forwards and opened. The 

 floor of the mouth is next raised so that air is forced into the 



FIG. 283. A, Lung of SaIiinui(li- 

 macu/oMti showing the regular ar- 

 rangement of the blood-vessels 

 extending between the individual 

 vesicles : this regularity is slightly 

 disturbed on the right side at f. 

 B, Lung of Rana temporaria, in 

 which the blood-vessels and vesicles 

 have a more irregular arrangement. 

 (After Fanny Moser. ) 



Fit;. 284. DIAGRAM OF A SIMPLE 

 LOBULAR LUNG (FROG). (From 

 Oppel, after Renault. ) 



A, alveoli; a, artery; e, epi- 

 thelium of lung ; /, vesicles 

 lined by the alveoli ; O, glottis ; 

 *.(>.p, pleuroperitoneum ; /, 

 vein. 



lungs. After a pause, the glottis and nostrils are opened, and thus 

 expiration takes place. The mechanism is therefore that of a 

 force-pump. 



In many Salamanders (e.g. Salamandrina perspicillata, Typhlo- 

 molge, Amblystomatinae, Desmognathinse, Plethodontinse) the lungs 

 undergo a more or less complete degeneration, even though all 

 traces of the gills disappear. The fact that the floor of the mouth 

 is continually raised and lowered, as in other Amphibians which 

 possess lungs, indicates that a bucco-pharyngeal respiration takes 



