THE ELEPHAKT TEETHIHG ALL THE TIME. 2?5 



to be always teething. The following facts are partly based 

 on Cuvier, Owen, and Wm. Jacobs: 



The grinders, which are constantly in progress of destruction 

 and formation, are not deciduous in the ordinary sense, for they 

 succeed each other horizontally instead of vertically, and not 

 more than one wholly or two partially (one on each side in each 

 jaw) is in use at one time. As the fore part of the tooth in use 

 is worn away by attrition and its roots diminished by absorp- 

 tion, its successor pushes it forward (a movement that appears 

 to be facilitated by the direct backward and forward action of 

 the lower jaw), and a large part of the replacing tooth is in 

 use for some time before the first is entirely shed. Thus a 

 grinding surface is ready all the time. The milk teeth are cut 

 eight or ten days after birth, the upper preceding the lower, 

 and it is about two years before they are entirely displaced by 

 the second set. The second set is in use, but gradually dis- 

 appearing, from the second year to the sixth, when the third is 

 fully in position ; it in turn serves till the ninth year, when 

 the fourth set is in position ; and thus it continues to the end 

 of the animal's life 100 or even 150 years. Each succeeding 

 tooth requires at least a year more than its predecessor to be 

 completed. 



The grinders are remarkable for their size and the complexity 

 of their structure, the upper and lower teeth being much alike. 

 They are composed of ivory (dentine), enamel, and a large 

 quantity of cement. The crown is short in proportion to the 

 depth of the base or root, only a small part appearing above 

 the gum. In the Asiatic species the crown is composed of 

 transverse, vertical, enamel-plated dentine ridges, about half 

 an inch apart, and joined together by cement. The ridges are 

 nearly straight and are tooth-like in appearance. The ridges 

 are good indicators of age, the first set of teeth having 4, the 

 second 8 or 9, the third 12 or 13, the fourth 15, and so on to 

 the seventh or eighth, which have 22 or 23. In the African 

 species the crown is studded by lozenge- shaped projections in- 

 stead of ridges. A tooth of the elephant Columbus, an excellent 

 specimen, which may be seen in Worth's Museum (New York), 

 weighs 12 pounds ; its breadth is 7 inches (the aggregate of 

 the six back teeth of the horse) ; thickness, 2 ; length, 11. 



