12 



The Proboscidea — Mastodon. 



the nostrils ; from this peculiarity the name of the group 

 (Proboscidea) is derived. These animals have no canine teeth, 

 and in this character they resemble the Rodentia (rats and 

 rabbits). They have ever-growing incisors of very great size. 

 but never exceeding one pair in each jaw, and more often 

 present in one jaw only. These incisor teeth project largely 

 out of the mouth, and are commonly called " tusks " ; they are 

 of an elongated conical form, and generally curved. They are 

 chiefly made up of solid dentine, the fine elastic quality and 

 large mass of which have rendered it invaluable as "ivory," for 

 commerce and the arts, since the earliest historic records. 



Fig. 11. — Left upper molars of Vinotheriv/iU gigantemn (Kaup) ; J natural size; Middle 

 Miocene, Sansan iGers), France (after Gaudry). 



The molars or grinding teeth are few in number, but laro-e 

 and complex ; they differ from those of other orders of animals, 

 in being developed from behind forwards, not vertically to the 

 tooth in wear (except in a few cases as where a premolar 

 replaces the last milk-molar/ro?>i beneath) -. and the series lasts 

 until the animal attains extreme old ag-e. 



Fig. 12.— The first right lower true molar of Mastodon sivalensis (laic. & C'autl.) : § natural 

 size; from the Older Pliocene of the Siwalik Hill?, India. 



The Mastodons had, when young, a pair of niilk-tusks^or 

 incisor teeth) in the upper jaw. and in some species a pair in 



