VOL. LXXXIX.] PHILOSOPHICAL TRANSACTIONS. 521 



swallowed. In the elephant's tooth, from the largeness of its size, the parts are 

 more distinct, and more readily contrasted with each other; but in other animals, 

 even those of a small size, as the sheep, the different structures are readily detected. 

 It is singular that this structure should have escaped the accurate investigation of 

 the late Mr. Hunter; particularly as the formation of the teeth was one of the first 

 objects he employed himself on; and he continued to pursue it to the end of his 

 life, marking the varieties which occur in different animals. The cause of his 

 overlooking it was the following: in making preparations of horses' teeth, to show 

 the figured appearance on the grinding surface, he rendered them black by means 

 of fire, which did not affect the enamel, so that the white lines of the enamel were 

 beautifully distinct on the black ground; but the bony part and the substance of 

 the tooth were equally coloured, and had a uniform appearance. The examination 

 of these preparations led him to believe, that the horse's tooth consisted of only 2 

 substances, the tooth itself and the enamel. Under this impression, Mr. Hunter 

 examined the growing teeth of the horse, and found the pulp rising from the jaw, 

 and the vascular membranes passing down from the gum, into the spaces between 

 the portions of pulp; he was therefore led to conclude, that the pulp was for the 

 formation of the tooth, and that the membranes which came from the gum were 

 for the formation of the enamel. 



Having so fully explained, in the elephant's tooth, the real uses of these 2 parts, 

 it is not necessary to say more in refutation of this opinion, which is published in 

 Mr. Hunter's work on the teeth; but, injustice to the correctness of his other 

 observations, I shall subjoin his account of the circumstances under which the 

 enamel of the human teeth is formed, taken from the same work. He says, " the 

 pulps are surrounded by a membrane, which is not connected with them, except at 

 their root, or surface of adhesion. This membrane adheres, by its outer surface, 

 all round the bony cavity in the jaw, and also to the gum, where it covers the 

 alveoli. When the pulp is very young, as in the foetus of 6 or 7 months, this 

 membrane is pretty thick and gelatinous. We can examine it best in a new-born 

 child, and we find it made up of 2 lamellae, an external and an internal: the ex- 

 ternal is soft and spongy, without any vessels; the other is much firmer, and ex- 

 tremely vascular, its vessels coming from those that are going to the pulp and body 

 of the tooth. While the teeth are within the gum, there is always a mucilaginous 

 fluid, like the synovia in joints, between this membrane and the pulp of the tooth."* 

 This mucilaginous fluid, I have already asserted, deposits the enamel ; which is fur- 

 ther confirmed by the following experiments and observations. The complex tooth 

 of the elephant, being composed of 3 different structures, each of which has a 

 peculiar process for its formation, led to an inquiry whether the materials themselves 

 were different, or only differently arranged. To investigate this, Mr. C. Hatchett, 

 from a zeal to promote the pursuits of science by which he is distinguished, oblig- 



* Natural History of the Human Teeth, by John Hunter, p. 86. — Orig, 

 VOL. XVIII. 3 X 



