228 



EESPIEATIOB . 



the respiratory system, and the consequent augmented amount 



of respiratory process, by 

 which a larger extent of 

 membranous surface became 

 indispensable. The bronchi 

 in birds are continued into 

 the lungs, where they divide 

 into membranous tubes, 

 which permeate their sub- 

 stance; the deeper tubes 

 stand like organ-pipes, and 

 open into the superficial 

 tubes ; and all are covered 

 with small parietal cells, 

 upon which vessels are dis- 

 tributed ; the cells form very- 

 elegant, delicate microscopic 



e ^ ~t reticulations, and generally 



Fie. 240. A piece from that part of , , 



the Serpent's lung which is most scan- present themselves as six- 



tily supplied with vessels, magnified sided spaces, 

 four hundred times. The vessels here [ 389. The lungs of man 

 form a very beautiful rete, with wide and fa e ma mmalia are form- 

 meshes ; they have been successfully ed after another and a differ . 



injected with fine size and vermmon. , , , 



eiit type ; the trachea here 



divides and subdivides, like 

 the branches of a tree, into 

 finer and finer branches, 

 which at first contain carti- 

 lages in their constitution, 

 but which by and by become 

 membranous, and finally end 

 in blind sacculi, or rather 

 in hollow berry or bud-like 

 Fig. 241. Terminal vesicles of the and clustered vesicles (figs. 

 human lung, hanging to a branch of 241 and 242). The pulmo- 

 the bronchi as berries hang to their n i c ce }l s O f ma n and the 

 stalk, and distinct from one another. mamma ]i a consequently, 

 The figure is half a plan, and the mag- parietal, but termi- 



nifvmg power used very high. ^ _ ^ ^ from ^ 



Gth to the 18th of a line in magnitude, the majority of them 

 measuring between the 8th to the 10th of a line in diameter. 



