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April 8, 1851. 
Professor Thomas Bell, Sec. R.S., in the Chair. 
The following papers were read :— 
1. ON THE STRUCTURE OF THE TEETH OF THE AMERICAN AND 
Inp1An Tarirs. By Joun Tomes, F.R.S. 
(Mammalia, Pl. X XIX.) 
It is now upwards of fifteen years since the attention of physiolo- 
gists and comparative anatomists was drawn to the structure of the 
tissues which enter into the composition of the dental organs. In 
1678 Leeuwenhoek communicated a paper to the Royal Society, on 
the Structure of the Teeth and other Bones, in which he described the 
dentinal tubes. His researches, however, were not confirmed by sub- 
sequent observers, and indeed were almost entirely overlooked until 
the period to which I have referred. Purkinjé, in 1835, confirmed 
the correctness of Leeuwenhoek’s observations, at the time uncon- 
scious that the tubular structure of the dentine had been previously 
recognised. He also described the structure of the cementum. 
Prof. Retzius was in the same year engaged in examining the 
structure of the dental tissues, and published the results in 1836. In 
1837 Prof. Retzius published a work on the subject, the substance of 
which was in 1839 printed in our own language by Mr. Nasmyth. 
In the latter part of 1837 I was engaged in examining the dental 
tissues, at that time unconscious that the subject had occupied the 
attention of the German or Swedish anatomists. In June 1838 the 
results of my examination were read before the Royal Society. In 
September of the same year, Prof. Owen read a paper on the Structure 
of the Teeth, before the British Association. In 1840 the publication 
of Prof. Owen’s ‘Odontography’ was commenced, and completed in 
1845. In this work will be found descriptions of the structure of 
the teeth of animals belonging to each division of Vertebrata. 
In these various essays the authors agreed generally in the main 
facts of dental structure, and in each successive publication new facts 
were related. Judging from the amount which had been published, 
it might have been concluded that the subject was well nigh ex- 
hausted. Such however was not the case: many blunders, in the 
hurry which is incident to a new subject, had been committed and 
required correction, while many important facts had failed to be recog- 
nised. Prof. Owen pointed out that in the Order Edentata the teeth 
are destitute of enamel, while it is present in the other mammalian 
orders, with the exception of a few isolated cases. 
Having neglected the subject of dental structure for some years, 
in consequence of more urgent pursuits, in 1847 I again entered on 
the inquiry, which to me possessed great attractions, not only on 
account of various modifications which are to be found in the arrange- 
