[ 297 ] 
IX. On the Structure and Development of the Teeth of Ophidia. 
By Charles S. Tomes, M.A. Communicated by John Tomes, F.B.S. 
Received October 5, — Read December 10, 1874. 
It has been usual to regard the dentine as the most, and the enamel as the least 
constant of the dental tissues, the cementum in this respect occupying an intermediate 
position* — this relation being held to have been established as a matter of observation, 
no less than as a legitimate inference from the process of development. It has, however, 
been shown by Kolliker and Waldeyer in the case of mammals, and by Santi Sirena 
and myself in the case of Batrachia and Sauria (the present paper extending these 
observations to the Ophidia) that the enamel-organ is absolutely the first structure 
which can be recognized in the vicinity of a future tooth, and that the dentine-organ or 
“ papilla ” can only be recognized at a later stage. 
This very early appearance of an enamel-organ would seem to point towards the 
enamel being both more important and more widely distributed than would be indicated 
by the statement that “ the enamel is the least constant of the dental tissues ”f. I was 
not therefore much surprised to find that the teeth of all the Ophidia which I have 
examined, amounting to some ten genera, are coated with a thin layer of enamel. 
In point of fact the thin layer of transparent tissue upon the outside of the teeth of 
Ophidia described by Professor Owen and others as cementum, is not cementum, but is 
enamel ; and this conclusion I can support by evidence which appears to me indisputable. 
And not only must the generalization that “ dentine and cement are present in the 
teeth of all reptiles ” be abandoned, but, so far as my own observations go, the occur- 
rence of cementum in the class of reptiles is comparatively rare, and it is in association 
with exceptional conditions of attachment when it occurs at all. 
I believe that it would be a correct statement, as regards recent reptiles at all events, 
to say that the teeth of reptiles consist of dentine, to which is very generally superadded 
* Prof. Owen (Odontography, p. 22) says, “ The enamel is the least constant of the dental tissues ; it is 
more frequently absent than present in the teeth of fishes ; it is wanting in the entire order of Ophidia among 
existing reptiles ; and it forms no part of the teeth of Edentata and many Cetacea among Mammals.” 
Of the cement he says (p. 183), “ Dentine and cement are present in the teeth of all reptiles,” this state- 
ment being also indorsed by Giebee (Odontographie, p. xvii). 
t In Professor Huxley’s paper (Microsc. Journ. 1853) I find the following passage in a footnote : — “ Why 
should not it ( i . e. the dense exterior layer upon the teeth of the skate and the mackerel) be called enamel ? 
It has at least as much claim to this title as that of the frog.” 
Since finding that there is enamel upon Ophidian teeth, I have again examined the teeth of frogs (the bull- 
frog, HyJci, common frog), and believe that there is a very thin enamel layer upon all of them. 
