40 
EDWARD B. POULTON. 
that the section is very nearly at right angles to the long axis of the head, but 
a little further posterior on the left side, as is also indicated by comparison 
of this figure with the last. 
Fig. C. — The eleventh section. On the right side the entrance of the 
papilla is seen, although discontinuous in this section from the rest of the 
papilla. On the left side the entrance is seen, and the outer layer of the 
enamel organ at a different level. In this latter section the small outer cusp 
(o. c.) is shown ; no dentine is developed upon it. The large inner cusp is 
cut through on its posterior slope in the left tooth, and higher up on the slope 
near the apex in the right tooth. 
Fig. 7. — The twelfth section. The two teeth are very uniform, the small 
outer cusp being seen in both, and the large inner cusp cut low down on its 
posterior slope. The entrance of the papilla is also distinct. The dentine is 
cut somewhat obliquely, as in the left tooth of the previous figure. The 
thirteenth section is not figured ; it is incomplete on the left side, so that the 
tooth is absent ; while on the right the tooth is similar to that of Fig. 7, 
except that the inner cusp is cut at a still lower level. 
Fig. 8. — The fourteenth section. The entrance of the papilla is seen to 
have shifted towards the inner side of the base of the teeth ; the inner cusp 
is now cut through close to its base, while most of its contour is concealed by 
the enamel organ. An outer cusp is seen in this and in all the remaining 
sections of this tooth. 
Fig. 9. — The fifteenth section. The teeth are now seen in section between 
the two inner cusps, and no dentine is formed upon any part of the surface. 
The contour of the enamel organ and oral epithelium on the left side could 
not be completed. 
Fig. 10. — The sixteenth section. In both teeth the anterior slope of the 
second or posterior large inner cusp can be dimly seen beneath the enamel 
organ. 
Fig. 11. — The seventeenth section. The large cusps are now cut vertically 
through their apices in both teeth ; above the apices the epithelial nodule is 
seen on both sides (W.). In the eighteenth section, not figured, the posterior 
cusps are cut through on their posterior slopes, rather below the apices. 
In the nineteenth section traces of the posterior margin of the teeth is seen, 
and in the twentieth section either the extreme posterior margin of these teeth 
or the extreme anterior margin of the third teeth. 
These sections through the middle tooth (b) should be compared with the 
surface view of the corresponding tooth in the lower jaw (Fig. 16, b), bearing 
in mind that the large cusps are external in the latter. Except for this differ- 
ence, the sections indicate a great general resemblance between the teeth. 
The number of sections in which a small outer cusp is seen proves that there 
must be four or five of these structures corresponding to the appearance of 
the inner side of the posterior tooth (c), shown in Fig. 16. 
