Tue MicroscopicaL News 
AND 
NORTHERN MICROSCOPIST. 
No. 41. MAY. 1884. 
THE FORMS, ORIGIN, AND DEVELOPMENT 
OF THE, TEE LEE: 
By Parsons SHAw, D.D.S., (U.S.A.) 
(Continued from page 89.) 
LTHOUGH we have seen that the beginning of dental structures 
is in the scales of fishes, we have not now the time to trace 
the various modifications of the substances of which they are 
composed up to the teeth of the higher animals. Allowing for 
all the transitional forms, a tooth is generally composed of three 
hard parts, namely—the enamel, the dentine, and the cementum, 
and a soft structure called the pulp. Nowhere are these seen to 
more perfection than in the human teeth. 
The enamel is the hardest part of the animal body ; it varies in 
different animals ; it never has more than five per cent., and often 
scarcely a trace of organic matter, and it is chiefly made up of lime 
salts. It is often said to be structureless, but that I cannot admit, 
for the microscopist often discovers that patient investigation with 
better powers reveals structure where it was too readily assumed 
not to exist. If the enamel is treated with dilute hydrochloric 
acid, it is dissolved away in the axial parts, so that if the section 
be transverse a fenestrated mass remains. In carnivorous and 
omnivorous animals the enamel covers all that part of the tooth 
exposed in the mouth ; and it also covers the incisors, and flows, as 
we have seen, through the body of the molars of the herbivora. 
The dentine constitutes in the human tooth the central and prin- 
cipal part of the body to such an extent that if only this structure 
were left it would show the distinct form of the tooth. The dentine 
is everywhere penetrated by what are known as the dentinal tubes. 
_Each tube starts by an open circular mouth upon the surface of the 
pulp cavity, from whence it runs outwards towards the periphery 
of the dentine, which it does not usually reach, but breaks up into 
VOL. IV. 
