106 OSSEOUS SUBSTANCE OF TEETH. 
thought formerly, that they became elongated to form the dental 
tubes, and that the intertubular substance was merely intercellu- 
lar substance between these prolongations. But I was compelled 
to relinquish that idea in consequence of there being no such 
appearance in the human tooth, and because the explanation 
led to difficulties with respect to the teeth of the pike, in 
which, according to Retzius, an immediate transition of the 
dental into the osseous substance takes place. If one of the 
largest teeth in the lower jaw of the pike be sawn off, deprived 
of its earthy matter by means of hydrochloric acid, and 
then divided into thin longitudinal sections, the dental sub- 
stance will be seen to form a hollow cone, which is filled with 
osseous substance. The dental substance is transparent,and con- 
sists of fibres which have a direction from the point towards the 
base of the cone. Canals traverse the osseous substance, 
resembling the Haversian medullary canals of ordinary bone, 
only they are not so regular. The dental tubes then are con- 
nected with these canals of the proper osseous substance, and 
may be distinctly seen issuing from them in a funnel-shaped 
form. The canaliculi soon ramify in the dental substance, 
and, as they run across the thickness of the dental cone, inter- 
lace with the dental fibres. According to this view, the 
dental tubes would correspond to the medullary or Haversian 
canaliculi of bone, and not to the calcigerous canaliculi pro- 
ceeding from the osseous corpuscles. It appears impossible, 
however, to be assured of the right explanation of all the struc- 
tural relations of the dental substance, until its development is 
examined in teeth differing widely from each other in con- 
struction. 
c. Osseous substance of the teeth. 
This requires no particular explanation, as it entirely ac- 
cords with the ordinary osseous substance. 
Having examined in detail the tissues comprehended in this 
class, and compared them one with another, we have yet to 
consider the entire class in relation to those which have been 
previously discussed, and to observe how much our knowledge 
of the transformations which the cells are capable of under- 
going, has been advanced by the study of it. 
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