572 ORGANS OF RESPIRATION. 



cartilages and fibrous structure are continued along the 

 bronchi, and their ramifications, in the substance of the 

 lungs. The laryngeal cartilages, by the successive formation 

 and detachment of new elementary pieces, and the coalescence 

 of others, pass through every inferior vertebrated form to 

 the human type. The few simple laryngeal muscles and 

 ligaments of amphibia and reptiles, become necessarily 

 broken up into distinct parts, to form new muscles and 

 ligaments, with different attachments and different functions. 

 And thus, by a series of changes, complicated but uniform, 

 of which no limit has existed in the past conditions or can 

 be conceived in the future, the respiratory organs of animals 

 have arrived at the type of the human pulmonary apparatus, 

 by which his vital fluids are purified and replenished, his 

 muscular system is furnished with its capability of action, 

 his high temperature is preserved in every condition of the 

 surrounding element, and his means of oral communication 

 are established, which enable him to express his feelings 

 and his wants, to communicate his accumulated knowledge, 

 and to enjoy the most refined physical and intellectual 

 pleasures of which his nature is susceptible. 



