PROBLEMS OF HI'MAX DEXTITIOX 147 



filial progressive state, which has ah-eady been attaiiK^d by the 

 right half. In the latter there was no second premolar at all, 

 the dental lamina obviously having lost the faculty to produce 

 the germ from which this tooth should arise. On the left side, 

 on the contrary, the dental lamina had still produced this germ, 

 but it was not a strong one. Apparently it had undergone the 

 influence of the evolutionary process, in consec[uence of which 

 its developmental force was of a deficient quality. Hence the 

 growth of the tooth was somewhat abnormal. Therefore the 

 relation between the ccmditions in the two halves of the jaw is 

 this, that on the right side of the jaw the progressive variation 

 is complete, while on the left side the condition may be regarded 

 as a less complete representation of the same variation. 



Surely such cases are very misleading from a surgical point 

 of view. For the practitioner, wishing to bring the whole den- 

 ture into a regular and normal state, will extract the second 

 inilk molar on the left side, in oi'der to bring the second pre- 

 molar into its normal position. This treatment is fully justified, 

 but there is a great chance that he may extract the second milk 

 molar on the left side, when no premolar is lodged in the jaw, 

 and by this treatment an irremediable gap is made in the arch, 

 because, as mentioned above, the premolar is absent. This case 

 indicates to practitioners that they must take the precaution 

 never to extract a second milk molar before having proven the 

 presence of the substituting premolar. 



Before leaving this subject, I beg to compare hgure 28 with 

 figure 5. AjDparently there is a similar variation in both prepa- 

 rations, three molars standing on the left side, and in l)oth 

 cases a ])remolar is erupted on the inner side of the arch at a 

 point corresponding with the interstice between the first and 

 second molar. But the morphological significance of the two 

 premolars is different, for in the case of the Macacus of figure o, 

 it is the lost third premolar which reappears, and in the case 

 of the human denture of figure 28, the second premolar reappears 

 in a denture having the future construction, ^^'hen in coming 

 ages such a construction has become the normal condition, a 

 variation such as occurs on the left side of hgure 28 mav l)e 



