GENETIC TYPE AND THE ENDOCRINES 111 



as a homozygous F 2 bassethound-bulldog with hound typed 

 bone. Mistaken diagnoses between homozygous and heterozy- 

 gous conditions among the F 2 generation are sometimes due 

 to the complication resulting from differences in degree of 

 expression on different bone constitutions. The bone consti- 

 tution is inherited quite independent of the achondroplasia 

 Leg factor in the crosses we have made. 



Further facts relative to constitutional differences in bone 

 response are found by examination of the leg skeletons from 

 the several groups of F 2 hybrids. 



Leg skeletons of the F 2 bassethound-shepherd. In addition 

 to the segregation of factors for normal and achondroplasic 

 growth of the extremities in the F 2 generation of the basset- 

 hound-shepherd cross, there is some evidence for segregation 

 of hound and shepherd bone type. Plate 24 shows photographs 

 of six right front leg skeletons. The first is from a pure long 

 Legged German shepherd dog and the other five are from F 2 

 bassethound-shepherd hybrids. 



The first F 2 leg skeleton is an extracted recessive long witli 

 hone of almost exactly the same type as that of the pure 

 shepherd to the left. If these two long legs had been photo- 

 graphed on a straight base line they would show identical 

 Lengths and proportions. Other long legged F 2 animals of 

 this cross show a somewhat shorter, stockier leg approaching 

 the foxhound type. 



The third and fourth leg skeletons are classed as hetero- 

 zygous for short, genotype si, and are much like the skeletons 

 from the Fj. The bone types in these legs are somewhat 

 mixed, yet the third skeleton inclines towards the shepherd 

 bone type and has a longer, lower epiphyseal process on the 

 ulna, less rotation of the wrist with less abduction and a 

 slightly narrower scapula than does the fourth skeleton of 

 the group at its right, which is more hound bone in type. 

 The metacarpal and phalangeal bones of the foot in achon- 

 droplasia are shortened on the same comparative proportions 

 as are the other bones. Type differences among the feet of 

 the Fo hybrids can also be seen. 



