DENTITION. 487 



but, in the case of such permanent teeth as take the position oc- 

 cupied by the deciduous, there is, before the teeth protrude, a 

 pedicle, (Gubernaculum Dentis,) which passes from the alveolar 

 end of the sac of the permanent tooth to the sac of the decidu- 

 ous tooth; and even when the latter is fully formed and pro- 

 truded, the same pedicle may be traced to that part of the gum 

 surrounding the neck of the deciduous tooth.* At birth, the 

 rudiments of fifty-two teeth may be found in the two jaws; 

 and, as a general rule at that period, the rudiments of the per- 

 manent are more superficial than those of the deciduous; but 

 their position is subsequently changed, so that the first descend 

 while the latter ascend. t 



As the permanent teeth are preparing to protrude, the alveo- 

 lar cavities, in which they are contained, form orifices on the 

 internal surface of the jaw near the edges of the deciduous al- 

 veolar processes, and which are called the Alveolo-dental Ca- 

 nals, (Itinera Dentium.) Those for the incisor and canine teeth, 

 are just behind their corresponding deciduous teeth, and those for 

 the bicuspated near and somewhat behind the infant molares. 

 At this period, a bony septum separates almost completely the 

 two orders of alveolar cavities from each other, and there- 

 by prevents their mutual interference. 



The permanent teeth being thus formed in new and distinct 

 sockets, and being kept off' from the deciduous, it is clear that 

 the latter cannot be pushed out of their alveoli, as is sometimes 

 supposed, by the growth of the former; and if it did take place, 

 it would produce the great inconvenience of causing them to rise 

 up into the mouth, beyond the level of the other teeth. On the 

 contrary, the deciduous teeth are made loose by the removal of 

 their roots, which progresses till nothing but the neck is left, and 

 then the slightest force applied dislodges them from their posi- 

 tion on the gum. This decay of the root is not even affected, 

 according to Mr. Hunter, by the pressure of the rising tooth, for 

 the new alveoli rise with the new teeth, and the old ones decay 

 along with their decaying fangs; and when the first set falls 

 out, the succeeding teeth are enclosed by a complete bony sock- 

 et; from which it is evident that the change is not produced by 



* J. Cloquet, Anat. PI. XXII. fig. 16, 17. Serres, loc. cit. p. 109. 

 f- Serres. 



