110 DEVELOPMENT OF THE TEETH. 



If the pulp which produces them be destroyed from any 

 cause, they lose the little vitality that they may possess, become 

 foreign bodies mechanically retained in the living parts, and 

 sooner or later are thrown off. 



The teeth are distinguished from the common bony tissue, by 

 the absence of any demonstrable cellular or vascular parenchyma 

 in their composition, by their being in part exposed to the 

 contact of the atmosphere, whiah no bone can be without losing 

 its vitality, by the enamel which covers them externally, by 

 their successive evolution and renovation at certain periods of 

 life, and lastly by their wearing out, and being lost in old age, 

 whilst the vital actions are still going on in the rest of the economy. 

 In many of the lower animals the teeth are evidently a 

 production of the skin or dermoid tissue, which is reflected in 

 at the commencement of the digestive passages, and many 

 modern anatomists have for the reasons above mentioned, con- 

 nected them with the description of the digestive organs. They 

 have, however, again been restored for purposes of convenience 

 to the student, to their proper connexion with the bones in which 

 they are developed. 



Development of the Teeth. 



The teeth, as we have before observed, are developed on a 

 principle different from that of other parts of the body, by 

 germs or gemmules. If the jaws of a foetus are examined with 

 care, even at the period of two months* after conception, an 

 extremely soft, jelly-like substance is seen lying in a groove 

 along the edge of each maxillary arch. At the third month it is 

 more consistent, and two plates of bone have sprung up at its 

 sides, which are the rudiments of the external and internal alveo- 

 lar plates. Shortly after this period, the pulpy substance sepa- 

 rates into distinct portions, and rudiments of the transverse plates 

 of the alveoli are seen shooting across, from side to side. These 

 distinct portions of the pulpy substance, have a papillary form 

 and are the germs or rudiments from which the teeth are devel- 



found after its extraction an abscess in the very centre of the bony structure, 

 communicating with the natural cavity and filled with pus. p. 

 * T. Bell. Beclard. 



