LUNGS VOICE 



47 



smaller in comparison than the right, and there is no pulmonary- 

 vein. The auricular septum has a large aperture, the communi- 

 cation between the auricles being larger than even in Necturus 

 (which breathes essentially by gills). The sinus venosus, instead 

 of opening into the right auricle only, opens more freely into 

 the left than into the right, and the latter communicates more 

 directly with the ventricle than the left, instead of about equally. 

 In short, the heart of these creatures appears almost bilocular, 

 instead of being trilocular, at least functionally. 



The lungs of the Urodela are always simple, extremely thin- 

 walled bags. They are highly developed in the Anura, the walls 

 being modified into numerous air-cells, whereby the respiratory 

 surface is considerably increased. The lungs are filled with air 

 by the pumping motion of the throat while the mouth is closed, 

 the nostrils being provided with muscular valves. A muscular 

 apparatus assists the filling of the lungs in the Anura. 1 



Most, if not all, Anura and some Urodela have a voice pro- 

 duced by the larynx, which, especially in the Anura, is provided 

 with a complicated cartilaginous and muscular apparatus and 

 with vocal cords. The voice 

 of the Urodela is at the best 

 a feeble squeak. The females 

 of the Anura are either mute 

 or they produce a mere grunt, 

 but that of many males is 

 very loud, and, moreover, in 

 many species it is intensified 

 by vocal sacs which act as 

 resonators. These sacs are 

 diverticula of the lining of 



the mouth-Cavity, and bulge Rana esculenta, B, Bufo calamita (cf. Fig. 52, 



,, , . -, p. 269). Ch, Choana, or inner nasal opening ; 



OUt the OUter Skin and the ^ opening of the Eustachian tube ; S, slit 



muscles, chiefly the mylo- leading into the vocal sac ; T, tongue ; Vo, 



JL. patches of teeth on the vomers. 



hyoid, of the throat. The 



nostrils and the mouth are firmly closed during the croaking. 

 " The sacs are called internal when they are covered by the 

 unmodified gular integument, however much this may be dis- 

 tended ; external when their membrane projects through slits at 



B 



FIG. 6. Internal view of the mouth of A, 



1 For the mechanism of the frog's respiration, see Gaupp, Arch. Anat. 1896, 

 p. 239. 



