2G2 
Transactions of the Society. 
8th. The evidences of the method of enamel formation as disclosed 
by caries of this tissue. 
9th. The bearing on various cytological problems of the facts 
elucidated under the foregoing headings. 
Our studies, you will observe, do not begin until the develop- 
ment of the tooth-germ has reached that stage where the formation of 
enamel is about to begin. It is at this point and at periods a little 
later that I wish to call your attention to the arrangement of the 
blood supply to the enamel organ. 
The enamel organ, during the earlier stages of its development, is 
bounded on both its internal and external aspects by a layer of cells 
derived from the columnar layer of cells of the mucous membrane. 
Between these two layers is the so-called “ stellate reticulum.” At 
the commencement of enamel formation the stellate reticulum forms a 
large proportion of the bulk of the tooth-germ; but, as development 
proceeds, this tissue gradually disappears, and the outer layer of 
columnar epithelium approaches nearer and nearer to the inner layer. 
In the meantime important changes have been going on in both the 
outer and inner layers of epithelial cells. The inner cells, originally 
composed of but a single layer, have divided into two, the outer of 
the two layers being called the stratum intermedium , while the inner 
layer constitutes the ameloblasts or enamel-forming cells proper. The 
importance or significance of the changes which take place in the 
layer of cells on the external surface of the stellate reticulum seems to 
me to have been largely overlooked. Outside of the external layer of 
epithelial cells is a kind of connective tissue, and in this connective 
tissue blood-vessels are developed at an early stage in the formation of 
the tooth-germ. When the development of blood-vessels has reached 
that stage in which they form a complete network surrounding the 
enamel organ, important changes are observed to be taking place in 
the layer of epithelial cells lying inside and close to this network of 
blood-vessels. A development of the cells takes place outwardly into 
the network of blood-vessels in the form of epithelial papillae. At 
about the time when these papillae are well developed, the stellate reti- 
culum has nearly disappeared, and the outer papillary layer of epithelial 
cells with the accompanying blood-vessels comes in contact and unites 
with the outer part of the inner layer of cells, or the stratum inter- 
medium. In the embryos of some animals, when this union of the two 
layers of epithelial cells occurs, the cells of the stratum intermedium 
are also entirely converted into epithelial papillae. In other embryos 
this does not occur, or only occurs to a limited extent. (See fig. 1.) 
Dr. Lionel Beale, the late Prof. Heitzmann, and, I believe, one or 
two others, claim to have seen blood-vessels developing in the “ stellate 
reticulum.” My studies of developing teeth extend over nearly twenty 
years, during which time I have never yet found a specimen showing 
the development of blood-vessels in the “stellate reticulum.” I have 
specimens, however, which I believe may possibly explain what has 
