GENETIC TYPE AND THE ENDOCRINES 



177 



DOES THE LENGTH OF JAW DIRECTLY DETERMINE TOOTH SIZE? 



Disharmony between the lengths of the upper and lower 

 jaws in certain types of dog skulls, a condition pointed out 

 in the previous section, made it seem desirable to compare 

 the sizes of teeth in the upper and lower jaws in order to 

 learn whether jaw size has a direct effect on tooth size. The 

 sum of the anteroposterior widths of the four premolar teeth 

 was selected as the most significant measurement, since the 

 extent of the premolar region of the maxilla differed more 

 than any other dental region in the various typed skulls of 

 comparable size. And, as we have seen, the premolar region 



3o- 

 2o- 



Text-figure 26. Sequence G. Sum of the anteroposterior dimensions of the 

 maxillary premolar teeth. Group of seventy skulls arranged in sequence from 

 greatest to least total dimension. 



of the lower jaw in certain breed types does not closely 

 follow such variations in extent of the maxillary premolar 

 region. Thus, a given skull may possess much abbreviated 

 maxillary premolar space while the mandibular premolar 

 space may be long and spacious. 



The sequence of skulls for this comparison was arranged 

 on the basis of the sum of the anteroposterior dimensions of 

 the maxillary premolars (text-fig. 26). The measurements 

 range from an extreme of 56 mm for total widths down to 



