680 BERTHA E. MARTIN 



3. Of the functional back teeth, the eighth has no predecessor 

 in the milk dentition. The other seven are replaced by perma- 

 nent successors. 



4. The functional back teeth of both dentitions develop nor- 

 mally. They are rootless, grow from persistent pulps, possess 

 normal tubular dentine, and a thin layer of enamel. 



5. The first, second, and eighth back teeth are one-cusped; 

 the others are bicuspid with a higher lingual and a lower labial 

 cusp. The first tooth is always one-cusped; the second and 

 eighth are bicuspid at first, but later become one-cusped through 

 the upward growth and obliteration of the original groove be- 

 tween the cusps. In the seventh tooth there appears a tendency 

 to suppression of the labial cusp. 



6. Of the non-functional front teeth, the sixth and last is the 

 only one which erupts, and it is shed soon after eruption. The 

 other front teeth are absorbed. 



7. The sixth is the largest of the front teeth, has the widest 

 deposit of enamel and is the only front tooth in which all of the 

 dentine is of the normal tubular variety. 



8. The other front teeth become increasingly smaller from 

 behind forwards and in somewhat over fifty per cent of cases, the 

 first tooth is represented by a degenerating enamel organ. The 

 relative thickness of enamel diminishes towards the anterior end 

 of the jaw until in the first two teeth it is so thin that it can be 

 definitely distinguished only with « the aid of an oil immersion 

 lens. In the anterior end of the jaw, there is also an increasing 

 tendency towards the formation of cellular dentine, and the 

 obliteration of the pulp cavity by the deposition of dentine. 



9. The formation of secondary tooth buds in connection with 

 these nonfunctional front teeth has not been conclusively demon- 

 strated. 



10. The dental formula of the lower jaw is probably M 1, Pm 

 7, C 1, I 6 or 5. 



11. In the maxilla there arise the anlagen of eight functional 

 back teeth whose structure and development is like that of the 

 corresponding teeth of the lower jaw. 



