THE ELEPHANT TEETHIXG ALL THE TIME. 275 



to be always teetliing. The following facts are parLly based 

 on Cuvier, Owen, and Wm. Jacobs: 



Tlie grinders, wliicli are constantly in progress of destruction 

 and formation, are not deciduous in tbe ordinary sense, for tbey 

 succeed eacb 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 

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

 appoarina-, from the second year to the sixth, when the third is 

 fully in i)osition ; it in turn serves till the ninth year, when 

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

 of tlie animal's life-103 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 louver teeth being much alike. 

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

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

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

 the o-um. In the Asiatic species the crown is composed ot 

 trans"xrse, vertical, enamel-plated dentine ridges, about half 

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

 nearly strai-ht and are tooth-like in appearance. The ndges 

 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 23 or 23. In the African 

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

 stead of ridcres. A tooth of the elephant Colambiis, 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 siY back teeth of the horse) ; thickness, 2^ ; length, 11. 



