382 CHARLES Et. STOCKARD AND A. L. JOHNSON 



the upper jaw is the decidedly modified part; the lower jaw 

 is much less modified in its proportions, and therefore pro- 

 jects forward beyond the shortened upper facial region. 



These facts may be finally emphasized by a consideration 

 of the upper facial index as charted in text-figure 77. It will 

 l»e recalled from previous references that this index is calcu- 

 lated in ;i reverse manner, length to width proportion rather 

 than width to length, and that therefore the long skulls have 

 high indices and the short skulls low. This again is a par- 

 ticularly good index for indicating clear differences between 

 skulls with normal occlusion and those with disturbed occlusal 

 conditions. 



The indicies for the normal group range in value from 74 

 to 124, while the indices for the three groups with partial 

 malocclusion range from 36 to 132, or higher than the upper 

 end of the normal range, although the large majority in each 

 of these three groups have facial index values entirely below 

 that for the normal group. Here again, the indices in group 

 E with complete malocclusion lie almost entirely below and 

 outside the range of those skulls with normal occlusion. 



From these several charts of skull indices it is clear that 

 the structural formation in localized regions of the skull 

 determines the type of dental occlusion, and that it is the 

 facial part of the skull which is of most importance in this 

 connection. The palatal index, as a direct expression of the 

 form of the upper jaw, is more intimately correlated with 

 the nature of dental occlusion than is the index for any 

 other skull feature. Modifications of the mandible in the dog 

 skull are much less pronounced than those of the maxilla, 

 and the responsibility of mandibular deformity for dental 

 malocclusion is largely secondary. There is considerable 

 probability that similar relations will be found to hold for 

 man, since the disturbances of facial growth in the human 

 infant and child are so readily comparable to the conditions 

 in the skull of the puppy. 



