IRREGULARITIES OF THE DENTAL APPARATUS. 751 



cavity capable of lodging a hen's egg, and in which is received a very- 

 elevated conical eminence on the fourth inferior molar. It will be 

 noticed that, in this case, the superior tooth is almost twice its normal 

 size, and is not square. This hypertrophy has not the characters of an 

 anomaly through fusion, as we have shown in the case of the incisors. 

 It is more probable that it is the result of a dental cyst, an opinion 

 which, if it were demonstrated, would also at the same time account 

 for the excessive volume of the tooth and the slight resistance of its 

 tissues to wear. 



" To recapitulate," says H. Bouley,^ " an important fact follows 

 from the preceding statements : when, from one cause or another, the 

 grinders of herbivora do not rub against each other regularly, on each 

 side, and over the whole extent of length and width of the surface of 

 the dental tables, the unequal wear, as a necessary and inevitable conse- 

 quence, causes, first, the deformity of the molars, and, later on, the irreg- 

 ularity, the imperfection, and, finally, the insufficiency of their func- 

 tion. This result is explained by the continual pushing out of the 

 teeth : in order that the latter phenomenon (poussee) may remain a phys- 

 iological fact it must be counterbalanced by a proportional wear ; then 

 will the dental organs be preserved in their proper conditions of form 

 and length, in order that mastication may be performed regularly. 



" But if this wear is unequal or less than what it should be, at 

 one point or another, either at the level of an isolated tooth, upon the 

 borders of the dental row, or upon the whole extent of the grinding 

 surface of this row, then the continued growth of the dental organs, or 

 of that part of them which is not worn off, will inevitably cause an 

 excess of their length. This being once accomplished, it cannot fail 

 to be exaggerated progressively, because mastication becoming so much 

 the more difficult as the masticatory apparatus is more imperfect, the 

 friction of the grinders against each other diminishes proportionally 

 to the degree of this abnormality. 



" Thus the tooth whicli is abnormally lengthened because a primary 

 cause prevented its regular wear, finding the condition of a new ab- 

 normal increase in the same excess of length which hinders the regular 

 action of the molars, one against the other, the effect produced becomes a 

 cause in its turn, and continues to produce similar effects ; whence these 

 deformities, often excessive, of the apparatus of mastication of which 

 we have just gis^en a description." 



All this shows us that an examination of the molar teeth should 



1 H. Bouley, loc. cit., t. iv. p. 625. 



