454 MKMOIRS OF THE CARNEGIE MUSEUM. 



small, simple-crowned, receives comparatively little wear, and is closely crowded 

 to the anterior faceof the succeeding tooth. D.Pa is proportionally longer and 

 narrower than P.. The configuration of the crown is otherwise c^uite similar in 

 the two. D.P3 has by far the greatest wear and is, if one may judge by the degree 

 of wear, the first cheek-tooth to appear in the young. D.P4 is less worn and cuts 

 the alveolar border simultaneously with or perhaps a httle sooner than D.P2. Back 

 of D.P4 are seen the points of the crown of Mi and back of the last-mentioned tooth 

 the alveolar border is deeply marked to indicate the position of M2 which is still 

 entirely buried in the jaw. 



5. The next stage of development in the succession of teeth from the deciduous 

 to the permanent series is interesting. Three individuals have been selected 

 which fairly well cover the main points in individual variation and irregularities of 

 development. Of these three individuals No. 1923a might be considered as the 

 most normal and will be first discussed. The small median incisor occupies the 

 usual position, while the permanent lateral incisor has broken through the alveolar 

 border (PI. LXVI, Fig. 5), uniting the alveoli for D.l2and D.I3 into a large trans- 

 versely oblongate fissure for receiving the cutting and procumbent incisor. ^^ In 

 this individual the alveolus for the canineof the right ramus is present, though very 

 small, while in the left there is no trace of an alveolus for the canine. D.Pi is in 

 place while D.P2 has been shed and the crown of Po appears through the alveolar 

 border. D.P.s is still in place butPs is well advanced and the deciduous tooth was 

 almost ready to drop off before the death of this individual. D.P4 is apparently 

 quite solid in the jaw and still served well for masticating purposes. Mi has 

 already received considerable wear, while M2 is almost entirely erupted. M3 is 

 quite undeveloped and is buried deep in the jaw. 



6. The next specimen to be considered is No. 1841, a pair of lower jaws. This 

 specimen presents some irregularities worthy of note. From the illustration 

 (PL LXVI, Fig. 6) it is seen that the permanent lateral incisors of this specimen are 

 retarded, i.e., they have not yet appeared above the surface of the alveolar border; 

 the alveoli for the canines are quite large. D.Pi is still in place, but contrary 

 to the specimen just described both D.P2 and D.P3 have disappeared and P2and P3 

 have already received some wear, D.P4 is solidly inserted in the jaw, Mi has been in 

 use for some time and is considerably worn as in No. 1923a, while M2 has received 

 slight wear on the anterior portion. M, on the other hand is apparently no further 

 developed than in the specimen previously described. 



'' In the judgment of the writer this incisor is probably I2 while I3 and the canine of the Diceratheres 

 are atrophied. 



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