HISTORY OF THE PROBOSCIDEA 



431 



had longitudinal bands of enamel, and in order to support the 

 weight of these great tusks the symphyseal, or chin, region of 



Fig. 228. — Head of upper Miocene tmastodon {fGomphotherium productum) showing 

 the chisel-like lower tusks. Restored from a skull in the American Museum of Natu- 

 ral History. 



the lower jaw was greatly elongated ; the molars had four 

 cross-crests. 



In the upper Miocene is found another and more primitive 

 stage of proboscidean development. In these species the grind- 

 ing teeth were three-ridged ; the upper tusks were quite short 

 and curved downward, diverging somewhat from each other, 

 and they had enamel bands. The lower tusks were still 

 shorter and of depressed, flattened and somewhat chisel-like 



