DEVELOPMENT AND SUCCESSION OF TEETH IN PERAMELES. 453 
the cartilage of the nasal floor (a/.) in this its most anterior 
portion. The upward inflection of the cartilage of the nasal 
floor is visible also in coronal sections some distance in front 
of the naso-palatine foramen. In serial sagittal sections, as 
one traces them outwards from the mesial plane, the dental 
lamina soon after its commencement is seen to become dis- 
tinctly thickened and enlarged. This enlargement extends 
outwards for some distance, and occupies a considerable por- 
tion of the anterior transversely lying portion of the lamina. 
This we take to be the representative of the first upper incisor, 
although there is as yet no differentiation of an enamel-organ 
distinct from the dental lamina, and therefore the tooth, as 
a distinct organ, cannot yet be said to have come into ex- 
istence. 
(It may not be out of place here at the outset to remark 
that, where we have given interpretations of the facts and 
phenomena observed [as distinguished from simple records of 
observations], these interpretations are expressions of judgments 
arrived at after careful collation of the facts, not only in the 
stage under notice, but in those both preceding and succeeding. 
An explanation may thus occur which would not be warranted 
by the facts noted in the immediate context alone.) 
Laterally to the swelling mentioned the lamina is again 
shallower and less bulky for a short distance. Soon, however, 
it again swells out to form an enlargement of considerably less 
transverse extension than the first. This we believe to be the 
representative of the second incisor. It is developed about 
the point where the lamina begins to bend backwards in a 
sagittal direction, as a comparison of coronal and sagittal sec- 
tions indicates. Immediately external to it (or behind it) the 
lamina bends much more acutely, and assumes definitely the 
general sagittal direction which it maintains during the re- 
mainder of its course backwards. And just at this acute 
portion of its curve the lamina expands rather suddenly into a 
large swelling, oval on cross-section, which is evidently repre- 
sentative of the third incisor tooth. This swelling is of con- 
siderable interest, because in connection with it we have a 
