562 
MR. TOMES ON THE STRUCTURE OF 
careful and repeated observations made upon upwards of 350 sections, cut from 
the teeth of various members of the order Rodentia, When a doubt as to the 
nature of a tissue has arisen, I have made numerous sections from different parts, 
and in different directions of the same tooth. In some instances I have made as 
many as twenty-five from the teeth of one species ; and have seldom contented 
myself with less than three sections. 
The conclusions which these researches justify depend mainly on the accuracy with 
which the observations have been made and recorded. 
Fortunately, preparations of dental tissues can be preserved for an unlimited 
period : hence my statements can at any time be tested by an examination of my own 
or corresponding’ sections. 
Those who will go over the field of observation through which I have passed, will 
I do not doubt justify me in the following conclusions ; — viz. That the teeth of some 
species of the order have specific structural characters by which they can be distin- 
guished from any other known teeth. That in the teeth of all the Rodentia, excepting 
the family Leporidae, a portion of the enamel has a lamelliform arrangement of its 
fibres. That the enamel lamellae have a different and distinctive character in each 
of the larger groups, and that the variety of structure is constant throughout the 
members of the same group ; we may take for examples, the Sciuridae, the Muridae, 
and Hystricidae, in each of which the structure of the enamel is different, and in each 
is highly distinctive. And that the varieties in the structure of the dental tissues, with 
a few isolated exceptions, justify and accord with the arrangements of the members 
of the order into the several divisions proposed by Mr. Waterhouse, and deduced by 
him from the relations of the several parts of the skull. 
The manner in which these various modifications in the structure of the enamel 
are brought about in its development, together with the adaptation of the varied 
forms of enamel-tissue to the wants of its possessors, will form the subjects of a future 
communication. 
Feh. 16, 1850. 
