The Senses 



205 



In all animals the mucous membrane which lines the 

 nasal cavity is very delicate and filled with nervelets. 

 These nervelets unite and form a single nerve on each 

 side which passes to the brain and transmits the impres- 

 sions derived from the odours in the air. The thin bones 

 within the nostril, which, in dogs and deer, curl and re- 

 curl in delicate lines and 

 scrolls and thus expose 

 such a large surface to 

 the odour-bearing air, are 

 but poorly represented in 

 birds. The simple curve 

 of the bone in the nos- 

 trils of birds is very simi- 

 lar in structure to that 

 found in reptiles. 



The question whether 

 vultures perceive their 

 prey by sight or smell has 

 been decided in favour of the former sense. Lacking the 

 ability readily to distinguish delicate odours, we find 

 among birds none of the glands which are so common 

 among hairy-coated creatures: the oil-gland is the only 

 one on the body, and this is practically odourless. But 

 slight as is the scent which diffuses from birds, it is 

 sufficient to enable a dog, with his wonderful keenness 

 of smell, to detect a crouching bird some distance 

 away. 



The woodcock of our inland swamps and marshes, 

 and the apterj^x of New Zealand, probably have the 



Fig. 149. — Turbinal scrolls of dog. In a 

 bird these bones are far more simple. 



