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- 

 roussa of Malaysia, the upper pair curve 

 upward and backward to the forehead. 

 The premolars and molars have two or 

 three roots or fangs ; in none of the lower *oxvh]g h tho enamel 

 vertebrates do the teeth have more than Crescents. -After 

 one root. 



The organs of sense are much developed, especially the 

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



Fig. 490. Crown of 



Fig. 401. Diagram of the labyrinth of the ear in J, the fish. //. the bird, and ///. a 

 mammal. U, utriculus; 8, sacculus: U8, utriculus and sacculus; Cr, caniilis n-unicns ; 

 R, recessus labyrinth!; UC, commencement of the cochlea, C . L. lagi'iia: A", circal 

 sac at the apex; C, ccecal sac of the vestibuluni of the cochlear canal. After Wai- 

 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 



