368 IVORY AND THE ELEPHANT 



of these ridges increased to three and then to four, until in 

 those of the Mammut americanum we have five such ridges. 

 Later still in the chain of development, the teeth of the 

 Stegodons offer from six to eight ridges. In the suc- 

 cessive elephant forms the multiplication of these ridges 

 becomes more and more noticeable. While in mammoth 

 remains recently discovered in Crete, Saline County, Ne- 

 braska (named Elephas hayi) there are ten ridges, the 

 teeth of Elephas imperator show eighteen, those of Elephas 

 columhi from twenty-four to twenty-six, and those of the 

 so-called "Hairy Mammoth" as many as twenty-eight 

 ridges. The peculiar growth of the teeth in the elephant 

 to which we allude elsewhere is not characteristic of the 

 very early ancestral forms. In the ancestral proboscidians 

 the teeth come up much as they do in other ungulates. 

 The milk premolars appear first, and then the molars come 

 up in succession behind them, permanent premolars pushing 

 up beneath the milk premolars as these wear down and 

 drop out. In the later types, with the shortening of the 

 jaw the premolars disappear, true molars pressing forward 

 as they come up, and successively replacing the teeth in 

 front of them as these wear down and fall out. Another in- 

 teresting change was in progress. The earlier teeth lacked 

 cement, but in the later mastodons a little began to appear. 

 In all of the mammoths the teeth are encased in and rein- 

 forced by a heavy outer layer of cement. 



Some mammoth bones of quite exceptional size have 

 been unearthed at Reynolds, Jefferson County, Nebraska. 

 The great thigh bone measures 5\ ft. in length, indicating 

 that this mammoth was perhaps the largest one so far dis- 

 covered.* 



*Erwiii H. Barbour, "Prehistoric Elephants in the Morrill Collections, the Nebraska 

 State Museum aud the University of Nebraska," in Sunday State Journal, Omaha, Jan- 

 uary 3, 1915. 



