Source : Webster's Revised Unabridged Dictionary (1913)

   Note: In all air-breathing vertebrates the lungs are
         developed from the ventral wall of the esophagus as a
         pouch which divides into two sacs. In amphibians and
         many reptiles the lungs retain very nearly this
         primitive saclike character, but in the higher forms
         the connection with the esophagus becomes elongated
         into the windpipe and the inner walls of the sacs
         become more and more divided, until, in the mammals,
         the air spaces become minutely divided into tubes
         ending in small air cells, in the walls of which the
         blood circulates in a fine network of capillaries. In
         mammals the lungs are more or less divided into lobes,
         and each lung occupies a separate cavity in the thorax.
         See {Respiration}.

   {Lung fever} (Med.), pneumonia.

   {Lung flower} (Bot.), a species of gentian ({G.
      Pneumonanthe}).

   {Lung lichen} (Bot.), tree lungwort. See under {Lungwort}.

   {Lung sac} (Zo["o]l.), one of the breathing organs of spiders
      and snails.