122 



ment of the components of the tissues in different animals, hut also 

 in minor modifications in the teeth of the same animal. 



My inquiries were first directed to human teeth ; the results, both 

 as regards structure and development, were published in my ' Lec- 

 tures on Dental Physiology and Surgery,' 1838. The teeth of mar- 

 supial animals next occupied my attention. In this order it was 

 found that the dentinal tubes are continued into and form a consider- 

 able portion of the enamel, excepting only in the Wombat. The re- 

 sults of these investigations will be found in the Second Part of the 

 'Philosophical Transactions' for 1849. 



By the help of this Society I have been enabled to make an ex- 

 tensive series of investigations in the teeth of the Order Rodentia, 

 with results which have far exceeded my expectations. Each family, 

 as arranged by Mr. Waterhouse, has its peculiar structure of enamel, 

 an account of which, with illustrations, is pubhshed in Part 2 of the 

 'Philosophical Transactions,' 1850. 



Having, by way of preface, given a very cursory and imperfect in- 

 dication of what has been done in dental structure, or rather of what 

 has been recognised as peculiar to certain groups of mammalian ani- 

 mals, in order to show that the subject is not without importance, I 

 shall proceed to lay before the Society certain peculiarities which I 

 find exist in the teeth of the two Tapirs, and which are, to the best 

 of my behef, confined to those creatures. It should however be under- 

 stood, that similar conditions may be found in the teeth of other ani- 

 mals, but at present I believe they have not been seen. I have 

 myself examined numerous examples from each of the mammalian 

 orders, and from the great majority of the genera, and have failed to 

 find a condition of dentine similar to that of the Tapir's tooth. Under 

 these circumstances, it may, I think, be fairly assumed to be charac- 

 teristic of those animals, and hence has a degree of importance which 

 it otherwise would not possess. With this impression, I have thought 

 it desirable that the facts should be recorded. 



The dentine of the molar teeth, when exposed by making a longi- 

 tudinal section through the centre of the crown and fangs, and re- 

 ducmg it sufficiently thin to be viewed by transmitted Hght, is seen to 

 be composed of tubes which pursue a uniform course. Those which 

 are destined to reach the highest parts of cusps or ridges pursue a 

 straight course, subject to slight undulations, while others, which pass 

 to the sides of the cusps, are turned in the latter part of their course 

 away from the central line of the cusps or ridges ; others again, which 

 pass to the lowest points of the depressions on the masticating sur- 

 face of the tooth, follow a tolerably straight course. The dentine 

 which forms the sides of the tooth is occupied by tubes which in the 

 outer third of their course describe a bold curve outwards, the con- 

 vexity of which is directed towards the crown of the tooth, but on 

 approaching the enamel turns a little upwards. In the fangs of the 

 teeth, the dentinal tubes, in addition to describing a double curve, are 

 subject to strongly-marked secondary undulations. The dentinal 

 tubes, as they leave the pulp-cavity for the crown of the tooth, have 



