THE EAR OF MAMMALS. 



563 



In the elephant the upper incisors form the 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 

 vertebrates do the teeth have more than 

 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 

 the tooth of a deer, 

 showing the enamel 

 crescents. — After 

 Owen. 



-zrs 



Pig, 491. — Diagram of the labyrinth of the ear in J, the fish. //, the bird, and III, a 

 mammal. U, utnculus; 5, sacculus; US, utriculus audsacculns; Cr, canalis reunieus ; 

 i?, recessus lahyrinthi; UC, commencement of the coclilea, O , L, lagena; K, coecal 

 sac at the apex; C, ccecal sac of the vestibulum of the cochlear canal. — After Wal- 

 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 



