374 CHARLES R. STOCKARD AXD A. L. JOHXSOX 



were made for comparative purposes. In plate 78 the two 

 photographs of each dog's teeth are placed side by side. 



Figure 1 shows the dental occlusion in 1422 9 . When the 

 animal was 6 months old, the teeth were full sized and the 

 lower canines were in normal occlusion, fitting between the 

 upper canines and lateral third incisors. The relative positions 

 of the teeth one year later are almost identical. Nos. 1417 $ , 

 1419 9 and 14145 (figs. 5, 6 and 7) show very similar con- 

 ditions of occlusion, and in each case there is little evidence 

 of any change having occurred to affect the relative positions 

 of the teeth during the 12 months which intervened between 

 the making of the first and second pictures. 



No. 1420 9 (fig. 2) shows a slight prognathism of the 

 mandible, as indicated by the projection of the lower incisors 

 in front of the upper. This condition in the young animal 

 is very mild and scarcely passes beyond an almost direct 

 opposition of the upper and lower incisors. The photograph 

 of the jaws at 18 months of age shows that as a result of 

 this slight malocclusion a definite spreading of the teeth 

 had taken place during the 12 month interval. Figure 4, 

 1418 9 , illustrates a closely comparable record. 



No. 14165 (fig. 3) shows a more advanced condition of 

 mandibular prognathism in the immature skull. Yet even 

 here the lower canines do not lie in front of the upper 

 incisors but rest against the third incisors at such an angle 

 as to prevent a complete biting closure of the teeth. At the 

 older age this condition has advanced and become somewhat 

 more pronounced, with the teeth more widely separated than 

 at the earlier stage. 



PLATE 78 



EXPLANATION OF FIGURES 



Growth of the jaws and final establishment of dental occlusion. Comparison 

 of second generation groat I)ane-St. Bernard hybrids at 6 months and 18 months 

 of age (one litter). 



1 1422$. 4 1418$. (5 1419$. 



2 1420$. 5 1417 c?. 7 1414^. 



3 141(5 <$. 



