many fragments of the teeth of the extinct Megatherium, Megalonyx,
Mylodon and Toxodon collected during his travels in South America.
Some of these fragments were in a state of incipient decomposition :
and my attention was forcibly arrested by the fact that these fragments,
instead of being resolved, like the fossil tusks of the mammoth
and mastodon, into parallel superimposed conical lamellae, separated
into fine fibres, arranged at right angles to the plane of the layers
which, according to the lamellar theory of dental structure, ought
to have presented themselves to view. I exhibited the most characteristic
of these specimens at my lectures on the teeth, at the
Royal College of Surgeons, in May, 1837, and stated that “ the
appearances which they presented were inexplicable on the lamellar
hypothesis | but that I should investigate the subject further, and
endeavour to elucidate the apparent anomaly before the following
session.” At the conclusion of that course, I had sections of these
fragments prepared for the microscope ; and stimulated by the amount
of clearly defined and beautiful structure which they exhibited, (1) 1
proceeded to examine similar sections of the human teeth and of
those of many of the lower animals. The excitement of the research
became heightened as the sphere of observation expanded, and I had
collected extensive materials for a Treatise expressly on the Structure
of Teeth, when the fourth number of Muller’s Archiv fur Physiologie,
for the year 1837, containing an Analysis of Purkinje s and Fraenkel’s
Treatise, came into my hands, in December, 1837, and awoke me from
the dream of discovery in which I had been indulging. I received,
shortly after, the fifth number of the same volume of Muller’s Archiv,
containing Dr. Creplin’s German Translation of the Treatise of Retzius,
(1) See Plates 79 and 84.
upon the perusal of which I abandoned my intention of publishing
those general observations on the structure of the teeth which I had
before deemed to be new, but now found to have been mainly anticipated
by Purkinje and Retzius.
I was not, however, discouraged by this disappointment, but,
feeling convinced that no work on the Comparative Anatomy of the
Teeth would henceforth be regarded as complete without an account
of the leading modifications of the dentinal tissue in the different
classes of animals, I proceeded to the microscopical investigation of
that tissue in many animals in which it had not been previously so
examined. The number of characteristic differences which presented
themselves, and which are described in the body of the present work,
led to the perception of the value of the microscopic structure of
the teeth as a test of the affinities of extinct animals, and to the institution
of researches into the laws of development of the dental tissues,
which, as then accepted and taught, were irreconcileable with the
general demonstration of the intimate structure of those tissues which
was yielded by the teeth of fishes, reptiles and mammals. (1)
The prelude to this generalization may be summarily recapitulated
as follows: the discovery of Leeuwenhoek that the dentine
was made up of very minute tubes, which proceeded from the inner
to the outer surface of the tooth, was confirmed by Purkinje, so far
as regarded their existence ; but Purkinje added an exact and particular
account of the direction of these tubes in the human dentine, and
showed that, in addition to them the dentine contained an interme-
(I) The chief results of these researches have been successively communicated to the
British Association at the Newcastle Meeting, August, 1838, (Transactions of the Association,
vol. vii, p. 135 ;) in the Proceedings of the Geological Society for 1838 and 1839, and in the
Comptes Rendus de l’Académie des Sciences, December 12, 1839.