354 CHARLES E. STOCKARD AND A. L. JOHNSON 



Plate 71 illustrates three of these jaw arrangements in 

 F 2 dachshund-Pekingese hybrids. To facilitate comparisons, 

 profiles of the long muzzled dachshund with normal dental 

 occlusion and the flat faced, short muzzled Pekingese with 

 fair occlusion are again shown. The F 2 s in figures 4 and 6 

 show r an extreme overshot condition, having a short Pekingese 

 lower jaw in association with a fairly long dachshund upper 

 jaw. Figure 3 has fortunately inherited an equally shortened 

 condition of both the upper and lower jaws, and in length 

 these are fairly intermediate between the dachshund and 

 Pekingese. The dental occlusion in this animal is also good. 

 Figure 5 shows prognathism of the mandible, the undershot 

 lower jaw in association with a shortened upper jaw; the 

 nose is slightly pugged, a character from the Pekingese. 

 The disharmony between upper and lower jaws in this animal 

 again causes complete dental malocclusion. 



Disharmonies between the growth reactions of two jaws 

 in the same head make it seem evident that the quality of 

 the endocrine environment cannot be altogether responsible 

 for the inhibition of growth in one jaw and stimulation of 

 growth in the other. It would seem logical to expect that a 

 modified internal chemistry would affect the simultaneous 

 growth of two related structures in much the same manner. 

 The old idea of a " developmental regulation" insuring har- 

 monious structural adjustments is also seriously questioned 

 by these evident contradictions. The commonly accepted 

 point of view of the embryologist that the upper and lower 

 jaws are derived from closely related branchial structures 



PLATE 71 



EXPLANATION OF FIGURES 



Further details of the jaw arrangements and dental occlusion to be found among 

 members of the second generation dachshund-Pekingese hybrids. 



1 Dachshund 1177 $. 3-6 F, hybrids. 



2 Pekingese 1118 <$. 3 2213 $ (normal dental occlusion). 



4 2212 c? (overshot). 



5 2094$ (undershot). 



6 2214$ (overshot). 



