568 PROBOSCIDEA. 



is used as a prehensile organ ; by means of it the animal convej^s 

 food to its mouth, uproots trees, and sucks up fluid, which it may 

 transfer to its mouth or squirt over its body. The ears are large 

 and there is a moderate tail. The tusks are enormously enlarged 

 rootless incisor teeth (^ 2) and in living forms are only present 

 in the premaxillae. In the mastodon there are also two incisor 

 teeth in the lower jaw which soon fall out in the female, but in 

 the male are retained as tusks. Incisor teeth are also present 

 in the lower jaw of Dinotherium where they have the form of 

 tusks, and of Tetrahelodon, Palaeomastodon and Moeritherium, 

 etc. (see below). 



The tusks consist mainly of dentine, being only tipped with 

 enamel in Elephas and ridged with the same substance in some 

 extinct species. They are preceded by milk teeth. There are 

 no canines in recent forms. The grinders are highly peculiar. 

 They are enormous elongated teeth with very numerous rows 

 of transversely elongated tubercles forming plates and com- 

 posed of enamel and dentine. The spaces between these tubercles 

 are in living forms filled with cement, and the grinding surface 

 presents in the worn tooth a number of transverse rhombic marks 

 consisting of dentine with an outer coating of enamel. In the 

 mastodon the cement is sparse, and the dental papillae are short 

 having the form of mammillary prominences (Fig. 294). In 

 Dinotherium, Palaeomastodon, Moeritherium, etc., in which there 

 is the ordinary succession, the molar teeth are bilophodont and 

 tapir-like, and there is no cement on the crowns.* In Stegodon 

 there are six to twelve transverse ridges, the valleys being partly 

 filled with cement. In Elephas (Fig. 293) tlie number of ridges 

 is much greater, increasing in the posterior teeth, so that the 

 last may have as many as twenty-seven. Witl\ this increase in 

 complexity, the crowns become longer, so that the brachydont 

 condition of the molars of Mastodon, Dinotherium and other 

 early forms gives place to a marked hypsodont structure. There 

 are altogether six grinding teeth in modern elephants on each 

 side of each jaw. Of these, three are either premolars which 

 have no predecessors, or deciduous molars which have no suc- 

 cessors ; the other three are molars. There are never more than 

 t' ree rarely more than two above the gum at the same time, 



* See pp. 512, 573. 



