210 



. COMPARATIVE ANATOMY. 



O 



FIG. 173. DIAGRAMS OF THE ORAL CAVITIES OF A FISH (A), AMPHIBIAN (B), 

 REPTILE OR BIRD (C), AND MAN (D). 



'N, external nostrils ; Ch, internal nostrils ; D, alimentary canal ; K, gill-slits ; L, 

 lung ; T, trachea ; 0, oesophagus: the arrow marked^ indicates the respiratory 

 passage, that marked B the nutritive passage ; t, the point where the two 

 passages cross one another. 



