226 



BESPIEATION. 



t 



Fig. 236. Lung of the water 



newt (Triton cristatus) : 



ditional space. When the dia- 

 phragm is again relaxed, and the 

 ribs are allowed to subside, the 

 cavity is again diminished, and 

 the air expelled. These move- 

 ments are termed-inspiration and 

 expiration. The spongy pulmo- 

 nary substance being thus dis- 

 tended with air, the blood sent 

 from the heart is brought into such 

 contact with it as to allow the re- 

 quisite interchange to take place. 

 [ 387. The minute anatomy 

 of the lungs, in vertebrate ani- 

 mals, exhibits many interesting 

 varieties. The structure is sim- 

 plest in the naked amphibia, 

 where it is but little more com- 

 plex than in the snails.* In the 

 water-newt, for instance, the 

 lungs present themselves as a 

 p a i r O f simple elongated sacs 



vein. 



'rf* X* & * % Iw&. ^ ; 

 C*/CV^B^^i^*.l 



W*%\f 



&ivV-*- 



A, the / fi 236), attached to an ex- 

 <-me ly short rudimentary la- 

 rynx, and internally exhibiting 

 no projection ; the air distends 

 the entire hollow internal sac, or 

 cavity. In the frogs the mem- 

 branous surface of the lungs is 

 increased by the development of 

 cells upon their internal aspects 

 (figs. 237 and 238), upon the 

 bottoms of which cells other secon- 

 dary and smaller ones can be per- 

 ceived ; all these pulmonic cells, 



Fig. 237. Portion of the lung 

 of the Triton cristatus* The ves- 

 sels are injected with fine size and 

 vermilion, and form so dense a net- 

 work that minute islets only of 

 j'-arcnrhvmn ro-""'" T-C^-I- 



* The lung presents itself in its 

 very simplest form in the snails and 

 slugs. The contractile respiratory ori- 

 fice here leads to a simple smooth in- 

 ternal cavity lined with a delicate 

 mucous membrane, upon which the 

 n"l r nnna r v vessels are distributed. 



