202 ON THB FOSSIL BONES OF PACHTDEEMATOTJS QUADRUPEDS. 



teeth, it is necessary to add one circumsfance to the description which 

 I have given of the germ : I reserved this point for the present mo- 

 raent, in order to avoid confusion. 



The base of this gelatinous body, (the productions of which, called 

 walls (murs) by me, ser\'e as nuclei for for the lamellae of the tooth) , 

 does Jiot adhere in all its points to the bottom of the capsule. There 

 are, from space to space, solutions of continuity, and consequently the 

 adhering parts of this base may be considered as very short pedicles. 

 When the lamella of bony substance has covered all the productions 

 or walls, and all the body of the nucleus of the tooth, it is always 

 continued upon and between the pedicles ; the parts of this lamella 

 which go between the pedicles, from the lower part of the body of 

 the tooth ; the parts which envelope the pedicles, and which are con- 

 sequently more or less tubular, form the first commencement of the 

 roots; 



These roots and the pedicles which ser\'e them as nuclei are then 

 prolonged, for two reasons: first, the progress of the lamellae of bony 

 substance, which, continually lengthening, force the tooth to raise it- 

 self and to make its exit from the alveolus ; then the thickening of the 

 body of the tooth by the formation of successive layers ; which, by 

 filling up the interior void, leave almost no more room for the gelatin- 

 ous nucleus, and press it towards the interior of the tubes of the 

 roots. 



There is neither enamel, nor cortical substance produced on the roots, 

 because the internal lamella of the capsule, which alone has the power 

 of secreting these two substances, does not extend so far. 



I conceive that it is partly to this absence of enamel, that we should 

 attribute the corrosion which commences on the roots as soon as the 

 portion of the crown corresponding to them has been worn down to 

 them. 



At this period the root has attained all the development which it 

 could attain; the pulpy nucleus is entirely supplanted by the layers 

 with which itself filled the cavity which it occupied. This force of 

 the growth of the root ceases then to counterbalance the growth of the 

 bony parietes of the alveolus, and the latter continually push out the 

 root. It commences to become carious, as soon as, escaping out of the 

 gum, it is exposed to the septic action of the air, of heat, and of the 

 moisture of the mouth. 



What gives, in my opinion, some probability to this idea, is, that 

 the corrosion commences sooner at the junction of the root and the 

 crown than at the point of the root. I have several proofs of it in 

 my specimens. One may judge of it also by the small tooth described 

 by M. Corse (Phil. Trans. 1799, tab. vi,/y. 3). Perhaps again the 

 mechanical compression which the root experiences on the part of the 

 alveolus contributes to its destruction, as we attribute the destruction 

 of the roots of the milk teeth to the pressure they experience by the 

 contraction of their alveolus, occasioned by the development of the 

 teeth which are to succeed them. 



Besides, it is always necessary that one part of these molecules should 

 be absorbed; but it would not be the only phenomenon in which a body 

 become foreign, would be taken up by the absorbents, and made to 



