IN THE LOWER ANIMALS, ETC. 251 



admirably adapted to aid the truncated snout in 

 turning up the earth. 



The sense of smelling is very acute in these 

 animals, and as it is omnivorous, not a root, 

 insect, or worm, escapes the olfactory sense — a 

 faculty which is turned to valuable account by the 

 truffle-himters of the Continent, who train the 

 hog to discover that delicate underground fungus. 



In the babyroussa, an animal closely allied to 

 the wild boar, the long and slender upper canines 

 describe a still more remarkable curve, and at a 

 little distance more nearly resemble horns than 

 teeth. They rise almost vertically through the 

 upper lip, and curve backwards until they some- 

 times pierce the skull. 



Although their use is not positively known, 

 they are not unreasonably supposed to be designed 

 as a defence for the eyes, when the animal forces 

 his way through the luxuriant undergrowth of the 

 tropical forests he inhabits. 



The air is admitted from the frontal sinuses 

 over a large portion of the diploe, or cellular 

 osseous tissue, between the inner and outer plates 

 of the cranium. 



The external surface is thus extended, without 

 increasing the weight of the head, a structure 

 which is still more extensively developed in the 

 enormous head of the elephant. 



In the hippopotamus the four upper incisor 

 teeth curve downwards, meeting the sides and 



