as indicative of the A(jc of the Animal. 
307 
producing organ of tlie enamel, and identical with both the per- 
formative and the adamantine membranes, these being, not two, 
but one ; 3rdly, That the pulpy mass lying external to the 
enamel membrane is the matrix of the crusta ; and 4thly, That 
produced ; c, the outer pulp with its vascular net-work of vessels ramifying 
amidst cells in a reticuled menibiane ; and d, the capsule. The close resemblance 
of this figure to one given by Todd and Bowman 
iu their J'/njsiologictd Anutomij, cannot escape the 
notice of the scientific reader. It is said by them 
that " the structiu-e of this thick pulpy mass is 
very beautiful and peculiar. It consists of a mesh 
of short fibres, meeting in numberless points, and 
at each point of junction a transparent clear nu- 
cleus is visible. It is elastic, spongy, loaded with 
fluid albumen, but destitute of vessels, and it seems 
perfectly distinct from that columnar structure 
which appears to be afterwards converted into 
enamel." — P/ii/sioloijical Anatomij, part iii., p. 175 
ct acq. What this " mesh of short fibres, meeting 
in numberless points," the " stellated bodies " of 
other observers, so accurately described by Todd 
and Bowman, may be, I do not presume to decide. 
Probably they are cells in a transition state from 
the ordinary epithelium of the mucous membrane 
to the cells of true crusta. 
With reference, however, to the pulpy mass being "destitute of vessels," much 
of the correctness of this depends on the stage of development when the examina- 
tion is made. Todd and Bowman could not detect any vessels ramifying in the 
pulp of a human /^e^us five months old, but they saw, even at that early date, loops 
of vessels descending from the membrane of the capsule upon the outer surface of 
this pulpy mass. In my description, and also in the accompanying figure, I have 
drawn attention to numerous vessels permeating the mass, but then it must be 
stated that my examinations were made on the permanent molar teeth of calves 
whose ages ranged from two to six months. It is the vascularity of the outer 
pulp, and which appears to be perfected in the latter stages only of the developing 
process, that alters the general character of the mass, and leads to its i\ltimate 
conversion into crusta. 
This view of the formation of the three structures will explain another well- 
known circumstance, namely, that the cnnen of a simple tootli, and likewise the 
cusps of a compound one, have upon them a mere ;film of crusta. By the time 
these parts are sufficiently covered with enamel the tooth is so far developed as to 
rise towards the under-surface of the gum. The resistance to its advance through 
this structure forces the outer pulp downwards towards the middle part of the 
body and also the fang. Under these circumstances the upper part of the capsule, 
through which the tooth is passing, adheres to the enamel membrane on the inner 
side, and to the gum on the outer. (See fig. 9 in the diagram, page 3ul.) The 
source of the supply of crusta, always the last formed of the three structures, is 
thus somewhat exhausted and hence a mere film of it, if any, is found on this part 
of the tooth. At first sight, this explanation may seem to be negatived by the 
fact that the enamel cups are filled with crusta, but a little reflection will at once 
remove the doubt. 
To render this more clear, I insert a figure representing a molar tooth in the 
act of cutting. 
Here it will be seen that although the enamel cmps, f, f, have penetrated the 
gum c, c, the latter is still pressing on the upper part of the enamel cups. This 
* Fig. 15. Vertical section of the capsule, pulp and enamel membrane, a, enamel 
prisms in the process of formation; b, the enamel membrane; c, the outer pulp; 
D, the capsule. 
Fig. 15.* 
