370 CHARLES I!. STOCKAKD AND A. L. JOHXSOX 



In plate 77 (fig. 1) the same lateral view of the F 2 basset- 

 lionnd-Saluki skull is again shown: the skull of a shepherd- 

 bulldog hybrid with the opposite, undershot, condition is 

 shown in figure 4. In the undershot skull, the face is short 

 and the upper jaw is wide, with the flaring teeth of the bulldog 

 in association with a long, strong mandible inherited from 

 the shepherd dog. The upper canine tooth is in front of the 

 lower canine in the overshot skull, while the prognathous 

 mandible of the undershot skull throws its tusk-like canine 

 tooth far in front of the upper canine. The common result 

 of both these ill arrangements is complete dental malocclusion. 



Exactly comparable conditions in the human are illustrated 

 by figures 2 and 5 of plate 77. Figure 2 is a plaster cast of 

 the dental arrangement in a case of maxillary prognathism 

 in a child. The upper incisors project far in front of the 

 lower, and all the mandibular teeth fall behind their proper 

 positions, causing complete dental malocclusion. This is the 

 overshot defect in the human and is similar in every detail 

 to the derangement in association of the jaws in the puppy 

 skull (tig. 1). These conditions in the child have been at- 

 tributed to various causes, such as thumb sucking during 

 babyhood, adenoid interference with nasal breathing, etc. 

 ( Vriainly no such causes underlie the condition in the puppy 

 and probably rarely do in the child. The inheritance of a 

 small lower jaw or defective mandibular development in 

 association with other types and proportions for the upper 

 jaw is to be suspected as a frequent cause of this dishar- 

 monious arrangement. 



PLATE 7 7 



EXPLANATION OF FIGURES 



Comparison of abnormal dental occlusion in two hybrid puppies with the same 

 c litions in the human. 



1 F, Saluki-bassethound 1908c? (overshot). 



2 Plaster east of overshot condition in a child. 



:; Plaster <-;ist of normal dental occlusion in the human. 



4 Backcross of F, bulldog-shepherd with bulldog 14o4$ (undershot). 



.". Plaster east of undershot condition in :i child. 



