422 



will afterwards become the first large grinders. They differ from those 

 that precede them in this, that they are to remain all life long, whilst the 

 primitive or milk teeth are lost at seven years old, in the same order in 

 which they appeared, and are replaced by new teeth, better formed, and 

 larger, excepting the small" grinders, and with longer and more perfect 

 roots. Towards the ninth year, two new large grinders appear beyond 

 the others. The child has then twenty-eight teeth, and dentition is com- 

 plete; though between eighteen and thirty, and sometimes much later, 

 the dentes sapientise, two to each jaw, show themselves at the extremi- 

 ties of the alveolar processes. 



The order observed in the successive cutting of the teeth is not so in- 

 variable, but it is frequently inverted. A child ten years old, now under 

 my care, cut the four first small grinders before the canine teeth. Den- 

 tition is in this, respect, like all other acts of the living economy : insta- 

 bility is its principal character. An attentive examination soon shows 

 how irregularly those phenomena proceed, whether physiological or pa- 

 thological, which appear the most to be subjected to calculable and de- 

 terminate periods*. 



This double range of successive teeth existed in the jaws of the foetus. 

 Each alveolar process, at that age of life, contains two membranous folli- 

 cles, lying one over the other. That which is to form the primitive tooth 

 swells the first, a calcareous matter covers its surface and forms the body 

 of the tooth, which invades also the follicle by which the osseous part is 

 secreted, so that the growth of the little bone being completed, the mem- 

 branous vesicle, in the parietes of which the dental vessels and nerves 

 branch out, is found in the centre of its body, and adheres to the parietes 

 of its internal cavity. It is difficult to say, why the growth of the dental 

 germs is successive $ why, in the seventh year, the primitive teeth are 

 detached, and are replaced by others which have remained so long buried 

 within the alveolar processes. Dentition is like all the other phenomena 

 of the living economy ; it is subject to endless varieties in its period and 

 duration, &c. Thus, teeth of a third set have been known to be cut iu 

 very old people. There are instances, but they are very scarce, of chil- 

 dren that have come into the world with two incisors in the upper jawfj 

 there are often supernumerary teeth, Sec. 



CCXXVI. Ossification. The process which goes on in the osseous 

 system, is not confined to the cutting and growth of the little bones which 

 are. attached to the two jaw 9.^ AH other parts of the skeleton harden; osse- 

 ous nuclei are formed in the centre of the cartilages, which hold the place 

 of the short bones of the carpus and tarsus ; the thickness of the cartila- 

 ginods substances, which separate the epiphyses of the bodies of the 

 long bones, is diminished ;- the large bones grow, and acquire solidity, 

 from the centre to the circumference. Those of the skull meet at their 

 edges, their fibres cross and form the sutures 5 the cartilaginous spaces, 



* See Erreurs populaires, sec : edit : Chap. 4. des Jlnnees climaleriques y et des Jours 

 critiques dans les maladies. 



f Louis XIV. was born in this condition. BAUDELOcauB observes, that the evolution 

 of some teeth, before birth, is not always connected with an extraordinary growth of 

 the infant; nor is it always a pressage of a stronger constitution. He endeavours to 

 prove this by several examples : these, however, may be regarded as exceptions only 

 from the general, and, we think, correct opinion on the subject. For some remarks on 

 the production of the teeth, see APFKSDIX, Note KK 



