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marks on the Dental System of the Mastodon, with an Ac- 

 count of some Lower Jaws in Mr. Koch's Collection, St. 

 Louis, Missouri, where there is a Solitary Tusk on the Right 

 Side, by William E. Horner, M.D., Professor of Anatomy in 

 the University of Pennsylvania," reported in favour of the 

 publication, which was directed accordingly. 



Dr. Horner inquires into the mode of formation of the teeth of the 

 Mastodon, and compares it with that of the elephant and of man. 

 The teeth of the Mastodon are all formed upon one type of configu- 

 ration, the number of denticules excepted ; they therefore, like those 

 of the elephant, do not admit of a division into incisors, cuspidati, 

 and molares, as in some other animals. The teeth are all molars. 

 The lower jaw itself resembles somewhat a human lower jaw cut off 

 in front of the molar teeth, and then joined in the two posterior seg- 

 ments. These teeth invariably succeed each other from behind ; the 

 hindmost, as they emerge, pushing the others forward, and out of 

 their places, until the latter all drop out, and a large solitary tooth is 

 finally left on each side of each jaw. 



Dr. Horner alludes to the erroneous nature of the early ideas of 

 naturalists on the teeth of the Mastodon, and observes that we now 

 know, with some degree of certainty, that the earliest teeth of this 

 animal were not more than an inch and a half square, and that the 

 three immediately succeeding were a gradual and successive enlarge- 

 ment on this and on each other's volume. In the Museum of Mr. 

 Koch, at St. Louis, there is a young head, the long diameter of which 

 is 18 or 20 inches, where the fact of four co-existent teeth on each 

 side of each jaw is exhibited. This specimen, with a dozen lower 

 jaws of different ages and sizes, enables us to trace, with some accu- 

 racy, the stages of dentition, until it reaches the large and solitary 

 grinder of ten inches in length on each side. Judging from these 

 phases of dentition, Dr. Horner infers that the entire amount of teeth 

 was at least 24; he is disposed, indeed, to think that the number may 

 have been greater than this; perhaps 28, and possibly 32. 



Dr. Horner makes some observations on some specimens of lower 

 jaws in Mr. Koch's Museum in St. Louis, in which there was a soli- 

 tary tusk on the right side, and alludes to the embarrassments that 

 their existence occasions in regard to the Tetracauledon of Godman ; 

 whether, for example, we are to consider them merely as abnormous 

 types of that animal, as known Mastodons, or as still another species 

 c 



