LUNGS 125 



authorities. One has recently said that a certain 

 Dinosaur inflates its hones to make itself float better. 

 The bones would be lighter if no air were in the hol- 

 low space. A balloon would soar better if no gas 

 were in it, provided it were stifl[ enough not to col- 

 lapse from pressure of the outside air. Nothing is 

 lighter than nothing. The only advantage in buoy- 

 ancy which the bones would have in getting air from 

 the lungs is that it is warmer, generally, than that 

 which might be infused from the outside, but this 

 slight expansion from heat is not appreciable. , 



Lungs, when present, are paired in all creatures, 

 except in the higher fishes, but in the long, limbless 

 reptiles, whether snakes or lizards, the left is often 

 a mere rudiment, and nearly always, except in one 

 family, is noticeably smaller than the right. The 

 AmjphisbcmidcB are the only vertebrates in which the 

 right lung is a vestige and the left one larger. 



This remaining lung is long and slim to suit its 

 space, and in serpents it runs far back. In the sea- 

 snakes it lies along the entire body-cavity, is large 

 and saclike at the rear, and stores such a quantity of 

 air that the creatures can remain long under the 

 water. In some reptiles the lungs are smooth sacs 

 inside — not pouched or cellular at all anywhere. 



The rule is that reptiles breathe by means of 

 compressing and expanding the ribs only, but in the 

 tortoise-forms these are fast to the shell, so that they 

 breathe in about three different ways, hinting of 

 ,irogs, birds, and mammals. They are the first crea- 

 tures in the scale to have a muscle lie under the 



