666 . BERTHA E. MARTIN 



cusped, and, during development, undergoes several conspic- 

 uous changes in shape (figs. 13 and 14). Some of the minor 

 alterations in shape are doubtless due to the obliquity with which 

 the sections were cut, but the change from a low, rather square 

 papilla with a wide pulp cavity to a round papilla with a narrow 

 entrance to the pulp cavity is unmistakable. The subsequent 

 widening out of the entrance to the pulp cavity up to a stage like 

 that shown in figure 14, and in text figure 10 is equally unmis- 

 takable. Its development is similar to that of the first back 

 tooth, except that the parts of the enamel organ are never so 

 well differentiated, the enamel pulp never forming a stellate 

 reticulum. Until the 71 mm. stage there is no conspicuous dif- 

 ference between its size and that of the first back tooth, but after 

 that stage, the first back tooth takes a rapid lead in size develop- 

 ment, while the sixth tooth leads in degree of development. 

 Thus the sixth tooth has received a slight deposition of enamel 

 in the 75 mm. embryo, while the first back tooth receives no 

 enamel until after the 78 mm. stage. The formation of odonto- 

 blasts and dentine also takes place first in the sixth tooth. At 

 birth, although much smaller than the first back tooth, it has a 

 relatively larger amount of dentine. As I have stated before, 

 this tooth may sometimes be found in the jaw several months 

 after birth (text fig. 3), and it probably erupts and is shed soon 

 after. 



The fifth tooth resembles the sixth tooth in its mode of devel- 

 opment. From the 71 mm. stage the sixth tooth takes the lead 

 in size and in each stage becomes increasingly larger than the 

 fifth tooth, so that at birth it is many times larger (text fig. 4, e 

 and d, 10, a and h). Deposition of enamel in the fifth tooth does 

 not take place as soon as it does in the sixth, and at birth less 

 has been deposited, and the enamel organ has likewise totally 

 disappeared. It goes through changes in shape similar to those 

 already described for the sixth tooth, although these changes 

 are here somewhat less marked. At birth it is also long and 

 narrow. The most interesting point in connection with this 

 tooth is the behavior of the odontoblasts. In the 71 mm. em- 

 bryo, when prodentine is beginning to form, some of the odonto- 



