THE 



MAMMAL*. 



563 



In the elephant the upper canines 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 rig. 490. Cro\vn of 



three roots or fangs ; in none of the lower 111 



showing the 

 vertebrates do the teeth have more than Crescent a. After 



one root. 



The organs of sense are much developed, especially the 

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



c 



Fig. 491. Diagram of the labyrinth of the ear in 7. the fish. IT, the bird, and 777. a 

 mammal. U, utriculus; 5, sacculus: US, utriculus and sacculus; Or, canalis reunions : 

 R, recessms labyrinthi; UC, commencement of the cochlea. C, L. lagcna: A', coecal 

 sac at the apex; C, coecal 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 minute, internal, and forms one of the internal 

 bones (malleus) of the ear. The labyrinth of the ear, 

 largest in fishes, is smallest in mammals. The cochlea 



