94 CHARLES R. STOCKARD 



becomes evident when the young puppy first attempts to 

 raise the body in order to stand or walk. The dislocated 

 limb or limbs are abducted by muscle pull and body weight 

 so that they project out laterally from the body. The puppies 

 are unable to maintain the limb or limbs in a vertical position 

 and sprawl in outspread fashion. When this deficiency in- 

 volves only one or two joints the animal gradually learns 

 to compensate for it by modifying the use of the other legs 

 and by redirecting the body weight. Such an animal may 

 later walk with the affected limb in normal position, its 

 muscles having strengthened and compensated so that almost 

 normal posture is developed. The skeletons of adult bulldogs 

 sometime show an old dislocation of the shoulder or hip joint 

 that was not apparent in the living animals. 



The F, hybrids of the bulldog-shepherd cross have shown 

 no symptoms of these articular deficiencies, but the number 

 of these hybrids studied is very small. 



Leg growth in the bassethound-bulldog F^ hybrids. Cross- 

 ing the straight long legged bulldog with the short legged 

 bassethound produces, of course, a very different leg condi- 

 tion from that found in the bulldog-shepherd hybrids dis- 

 cussed above. But the bulldog-shepherd experiment offers 

 confirmation of the belief that the modified leg in the basset- 

 hound-bulldog hybrids is inherited from the bassethound 

 parent only, with no contribution from the bulldog. Figures 

 4, 5 and 6 of plate 18 contrast the results of these two crosses. 

 Figures 5 and 6 show the bassethound-bulldog-hybrid in front 

 and lateral views. The legs are extremely achondroplasic, 

 short and much bent. In fact the condition in this hybrid 

 seems as fully pronounced as in the bassethound itself even 

 though the hybrid is heterozygous, carrying only the single 

 gene for leg chondrodystrophy. This exaggerated expression 

 is what forced us to test the bulldog against the shepherd 

 in order to determine whether the bulldog contained in its 

 genotype some factor or combination not evident in its pheno- 

 type but which would nevertheless give rise to achondro- 

 plasia of the long bones. After the negative results of this 



