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XXL On the Structure of the Dental Tissues of Marsupial Animals, and more especially 
of the Enamel. By John Tomes, Surgeon-Dentist to the Middlesex Hospital. 
Communicated by R. E. Grant, M.D., F.R.S., Professor of Comparative Anatomy 
and Zoology at University College. 
Received June 21, — Read June 21, 1849. 
My dear Dr. Grant, 
On making microscopic examinations of the teeth of one or more species of the 
several families of the marsupial animals, the skulls of which you kindly placed at 
my disposal, I found some peculiarities of structure, which so far as I know have not 
hitherto been recognised, and which will I think be found to constitute a pretty con- 
stant character in the teeth of this order of quadrupeds. It is my present purpose 
to describe these peculiarities, and should the communication seem sufficiently inter- 
esting and important to engage the attention of the Royal Society, my debt of grati- 
tude, already great, will be rendered yet greater by your lending your name for its 
presentation. 
Professor Owen, in his Odontography (p. 397), when treating on the structure of 
the marsupial teeth, says, The dentine, enamel, and cement of the teeth of marsupial 
animals, present the usual microscopic characters of these tissues in Mammalia.” 
My researches have led me to a different conelusion. The enamel presents a very 
strongly-marked peculiarity, common (so far as I have examined), with one excep- 
tion only, to all marsupial teeth, and present only in a very limited number of other 
mammalian teeth. I have hitherto found it only in the British Shrews, the Hyrax, 
and in the molar teeth of the Jerboa. 
The main peeuliarity to which I allude, is that the greater number, if not all, of 
the dentinal tubes are continued into, and constitute a considerable portion of the 
enamel. I have in another place* pointed out that in the human teeth the dentinal 
tubes are in small numbers, and occasionally only continued for a short distance into 
the enamel ; and the same may be said of many other teeth. In these instances how- 
ever the condition is rudimentary only, but in the marsupial teeth the development 
of the tubes in the enamel is as perfect as in the dentine itself. It is not difficult to 
suppose that a portion of the columns of cells, which constitute the enamel pulp, may 
become developed into tubes continuous with those formed by the columns of cells 
in the adherent dentinal pulp, instead of being converted into solid enamel fibres which 
* Lectures on Dental Physiology and Surgery, p. 35. 
