THE ATTACHMENT OF TEETH. 209 



which will serve to convey a good idea of its general cha- 

 racter. If the base of one of the teeth, with the subjacent 

 jaw-bone, be submitted to microscopic examination we shall 

 find that the layer of bone which closely embraces the tooth 

 contrasts markedly with the rest of the bone. The latter is 

 fine in texture, its lacunae, with their very numerous fine- 

 canaliculi, very regular, and the lamination obviously refer- 

 able to the general surface of the bone. But the "bone 

 of attachment" is very coarse in texture, full of irregular 

 spaces, very different from the regular lacunee, and its lamin- 

 ation is roughly parallel with the base of the tooth. The 

 dentine of the base of the tooth also bends inwards (Fig. 89), 

 and its tubes are lost in the osseous tissue, a blending so- 

 intimate resulting, that in grinding down sections the tooth 

 and the bone of attachment often come away together,, the- 

 tooth and this bone being more intimately united than this, 

 special bone is with that of the rest of the jaw. 



A study of its development also proves that it has an in- 

 timate relation with the tooth with which it is continuous, 

 for it is wholly removed with the fall of the tooth, and is. 

 specially developed again for the next tooth which comes, 

 into position. The periosteum of the rest of the jaw-bone^ 

 appears to take an important share in the formation of this, 

 special bone substance, and the tooth capsule, by its ossifi- 

 cation, apparently contributes little. 



In the frog the teeth are commonly described as being 

 attached by their bases and outer surface to a continuous 

 groove, of which the external wall is the highest. Such is, 

 however, an inadequate description of the process, the- 

 tooth, as seen in section, being attached on its outer side 

 by a new development of special bone, which extends for a. 

 short distance up over its external surface ; and for the 

 support of its inner wall there springs up from the sub- 

 jacent bone a pillar of bone, which is entirely removed when 

 that tooth falls, a new pillar being developed for the next tooth. 



