CENOZOIC ERA 



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skull is hinged to the vertebral column by the occipital condyles, which 

 thus constitute the fulcrum of a lever system. Increasing the height of the 

 head above these condyles increases the surface for, and the mechanical 

 advantage of, the muscles and ligament which support the head. The 

 importance of achieving such mechanical advantage is evident when we 

 recall that the two tusks together may weigh over 400 pounds and be 9 or 

 10 feet in length, though the average size is not so great as this. 



FIG. 10.10. Molar tooth of elephant. A, crown view. 

 B, longitudinal section. Black, enamel. Oblique lines, 

 dentine. Dots, cement. (From Lull, Organic Evolution, 

 p. 563. Copyright 1945 by R. S. Lull. Used by permis- 

 sion of The Macmillan Company, publishers.) 



The tusks are formed from the right and left second upper incisor teeth. 

 The ivory composing them consists of the dentine material of the teeth, no 

 enamel being present except for a small area on the end of the tusk when 

 it first erupts. A large, open pulp cavity in the base of each tusk provides 

 for continuous growth. 



Nothing about an elephant is more unique than its molar tooth structure 

 and the system of molar replacement. Each individual molar is large, 

 consisting of several flattened plates arranged vertically and fastened to- 



