XIV INTRODUCTION. 



many fragments of the teeth of the extinct Megatherium, Megalonyx, 

 Mylodon and Toxodon collected dm'ing 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 frag- 

 ments, 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 cha- 

 racteristic 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 Miiller's Archiv fur Physiologic, 

 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 num^ber of the same volume of Miiller's Archiv, 

 containing Dr. Creplin's German Translation of the Treatise of Retzius, 



(1) See Plates 79 and 84. 



