SPECIAL ORGANS. 91 



snout that they are employed in exercising the sense of 

 touch, as in whiskers (vibrissse) of many quadrupeds. 



ORGANS OF SMELLING. 



Many Invertebrata possess the sense of smell ; but with 

 them no organs have been definitely assigned the function.* 



YERTEBRATA. Pisces. The nasal capsules, two in num- 

 ber, are placed one upon either side, on periphery of body, 

 commonly at a point midway between the eye and snout. 

 Each consists of a depressed rounded chamber, lined with a 

 very vascular plicated membrane, and in some cartilaginous 

 forms covered with ciliated epithelium. Nose rarely com- 

 municates with palate, f 



Batrachia and Reptilia. Nasal apparatus, in common with 

 all Yertebrata above fishes, is contained within a diverticu- 

 lum from respiratory canal. In Proteus the peripheral por- 

 tion is plicated, as in fishes, but opens upon palate, behind 

 upper lip. Region of turbinated bone cartilaginous. With 

 others, olfactory nerves are distributed upon the mucous 

 membrane lining the anterior portion of the ' girdle bone ;' 

 and are separated from one another by a median partition. 

 In Crocodilia the anterior nares may be closed by muscular 

 action. In Ophidia, turbinated bones rudimentary; nasal 

 glands present. 



Aves. Anterior and posterior nares well defined; latter 

 often unite to form a single opening, covered with protecting 

 papillae. The turbinated bones are larger than in reptiles, 

 though the convoluted portion of the ethmoid is yet but par- 

 tially ossified. Conspicuous nasal glands constantly present. 



* To the antennae of insects have been assigned the double function of 

 smell and hearing. There can be very little doubt that the former sense is 

 so situated, and, by the diversity of form of the small fossits seen, it is pos- 

 sible that those of a larger size and greater depth pertain to hearing. (Horn.) 



f There is great reason to believe that, suited to their surrounding ele- 

 ment, the nasal capsules of fishes are much more sensible of odorous bodies 

 dissolved in water, and applied by its medium, than we should be if the 

 application of the object was to be made to our organ of smell by the same 

 medium. (Monro.) 



