ORGANS OF THE SENSES. 293 



by enlarged nasal cavities which open posteriorly both by 

 a common orifice on the median plain, near the anterior 

 part of the palate. These cavities are increased in the 

 sauria where the turbinated bones begin to be strengthened 

 by ossific matter and to assume a more convoluted form. 

 They extend from the point of the muzzle nearly along the 

 whole head, separated by the vomer, in the alligators, 

 gavials and crocodiles, where they generally open externally 

 by expanded, contractile, valvular sacs, as in many cetacea. 

 The anterior and posterior openings of the nares, in the 

 saurian reptiles, are wider than in the ophidia, the whole 

 organs are situate more internally and are more protected 

 by the expanded nasal bones. The whole organs of 

 smell are still more covered and concealed by the osseous 

 walls in the consolidated head of the chelonian reptiles, 

 where the olfactory surface is encreased in extent, the 

 anterior nares are very small, and the posterior openings 

 are placed further backward from their primitive anterior 

 position in the inferior vertebrata. 



The olfactory nerves and the whole internal organs of 

 smell are comparatively small in birds, and their imperfect 

 development of this sense is compensated for by their high 

 powers of vision, which is better adapted for their active 

 life and the great distances at which they generally require 

 to distinguish their food. The exterior openings of the 

 nostrils are generally large and oblique for the more free 

 respiration required during their rapid movements; they 

 perforate the horny mandible or the cere, or the feathered 

 skin, and the various forms and positions of these exterior 

 openings present useful characters for the distinction of 

 species in this class. There is commonly a nasal gland of 

 considerable size in or near each orbit. The cartilaginous 

 alae of the nose are seldom moveable or prolonged, the 

 septum is often more deficient below than that between 

 the orbits, and the posterior nares, prolonged backward to 

 near the glottis, often terminate by a single opening covered 

 with protecting papillae. The turbinated bones are larger 

 than in reptiles, and the convoluted portion of the ethmoid, 

 though they are still but partially ossified, and the olfactory 

 nerves pass from their long ethmoidal tubes, through the back 

 part of the orbits, into the convoluted plate of the ethmoid. 



