THE EAR OF MAMMALS. 



563 



In the elephant the upper incisors form thb tusks, the cor- 



responding teeth of the lower jaw being absent. In many 



teeth, as those of the deer (Fig. 490), the 



crown of the molars is quite convex, with 



crescent-shaped enamel areas. The canines 



are large and sabre-shaped in the cat fam- 



ily, while in the pigs, especially the baby- 



roitssa of Malaysia, the upper pair curve 



upward and backward to the forehead. 



The premolars and molars have two or 



three roots or fans in none of the lower 



Pig. 490. Crown of 



vertebrates do the teeth have more than Descents. After 

 one root. 



The organs of sense are much developed, especially the 

 ear. The quadrate bone of the reptiles and birds, which is 



Fig. 491. Diagram of the labyrinth of the ear in 7. the fieh. II, the bird, and 7/7. a 

 mammal. U, utriculus; S, sacculus; Uft, utriculus and sacculus; Cr. canalia renniene : 

 7?, recessus labyrinth!; UC, commencement of the cochlea. C, L, lagena: A", coecal 

 pac at the apex; C, coecal sac of the vestibulum of the cocnlear caual. After \\'a.l- 

 deyer, from Gegenbaur. 



large, external, and suspends the lower jaw to the skull, 

 now becomes much changed, and forms the zygomatic 

 process of the squamosal bone. The labyrinth of the ear, 

 largest in fishes, is smallest in mammals. The cochlea 



