376 CHARLES R. STOCKARD AND A. L. JOHNSON 



This series of photographs would indicate that the type of 

 dental occlusion is about completed at the time permanent 

 dentition is fully established, which is, in the dog, at about 

 6 months of age ; at this time the animal is also approaching 

 sexual maturity. But slight changes in the position of the 

 teeth and their relative arrangements may occur after this 

 time. The most extreme cases of mandibular prognathism 

 may, in some bulldogs, continue to increase gradually up to 

 about 15 months of age. 



RELATION OF DENTAL OCCLUSION TO SKULL INDICES 



On the basis of degree of dental occlusion, a collection of 

 184 adult skulls from different pure breeds and hybrids has 

 been separated into the following seven groups: Group A, 

 forty-nine skulls with normal occlusion; group B, seventeen 

 skulls with malocclusion of a few individual teeth; group 

 C, seventeen skulls with incisors meeting in end to end op- 

 position; group D, sixty skulls with mandibular incisors 

 in front of the upper (undershot) ; group E, twenty-nine 

 skulls wdth the entire mandibular series of teeth anterior 

 to the proper position (undershot) ; group F, five skulls with 

 the mandibular incisors or molars, or both, posterior to the 

 normal position relative to the upper series (overshot) ; and, 

 finally, group G, seven skulls with poor, irregular occlusion. 

 The values of the five different skull indices were plotted 

 for these seven occlusal groups in order to find whether definite 

 relationships could be established between a given skull index 

 or shape and the state of dental occlusion. 



Text-figure 72 indicates the values for the total skull index 

 of the individual skulls in each group. The total skull index 

 expresses the relation of width across the zygomatic arch 

 to entire length of skull base from foramen magnum to 

 end of premaxilla, and is, therefore, low for long skulls and 

 high for short. The skulls with normal dental occlusion range 

 in total index from 72 down to 52 and may all be considered, 

 on the basis of such indices, long, narrow skulls. The three 



