Development , &c. of Dental Enamel. By J. L. Williams. 263 
been regarded as a discovery. The connective tissue lying outside of 
and adjoining the stellate reticulum, being separated from it only by 
the single layer of epithelial cells referred to, is often so like the 
stellate reticulum in structure as to be easily mistaken for it under 
certain circumstances, even by an expert. It is in this connective 
tissue, which so closely resembles the stellate reticulum, that the 
blood-vessels are always developed. By some very slight displace- 
ment the two tissues might come into actual contact, and thus an 
error with reference to the point mentioned would easily arise. 
The papillary arrangement of the cells of the stratum intermedium 
reaches its highest point of perfection in the persistently growing 
incisor teeth of the rodents. Here all traces of the stratum inter - 
medium, as it has always been figured, completely disappear ; and in 
its place we have an arrangement of papillae interlocked with loops of 
capillaries and with larger blood-vessels lying in immediate contact 
with the outer end of these papillae. (See fig. 2.) 
The structure of completely formed enamel is, as we shall see, 
made up of two distinct features. I shall be able to show you clearly 
that the enamel rods or prisms are not composed of a single homo- 
geneous substance, as has always been supposed, but that the basis 
or substructure of these rods is distinctly fibrous or granulo-fibrous. 
Into this fibrous matrix the calcific material is deposited. I believe 
there is the strongest possible evidence, short of absolute proof, that 
this calcific material of enamel, which is first deposited in the form of 
an albumen-like fluid, is secreted from the blood-vessels by the papil- 
liform arrangement of epithelial cells which constitute the stratum 
intermedium. We must think of this material as drawn from the 
blood-supply by cell action. Now, the ameloblasts, which have 
heretofore been regarded as vested with the entire- function of enamel 
formation, are nowhere in contact with the blood-vessels. Lying 
between them and the blood-supply we always find the cells of the 
stratum intermedium. If, then, we regard the ameloblasts as the 
sole enamel-formers, we must think of them as somehow drawing 
the enamel material from the blood-vessels through the completely 
passive layer of cells known as the stratum intermedium — an ex- 
tremely improbable phenomenon. 
In the absence of positive proof, the highest probability always 
stands as the strongest form of evidence ; and the highest probability 
seems clearly to be that the cells of the stratum intermedium are the 
first active agents in selecting the calcific material for enamel building 
from the blood. The gland-like papilliform arrangement of these 
cells strongly suggests the function, and their immediate contact with 
the source of supply makes the evidence almost positively conclusive. 
It is, of course, highly probable that the albumen-like calcific material 
undergoes some modification in passing through the ameloblasts, but 
their function with reference to this material is, at most, secondary. 
(See fig. 3.) 
