76 HEREDITY AND EUGENICS 



adult is shown by the fact that the mere tension of the 

 muscles or weight of the body, as in dancing, may be 

 sufficient to cause a fracture. Twins may be born 

 in families having the peculiarity, one showing the 

 defect and the other normal. Sedgwick (1863) cites 

 a family from Dr. Pauli with a less extreme form of 

 the condition, in which the brittleness was confined 

 to the bones of the upper extremities. It occurred in 

 three generations. 



Digital Abnormalities. 



We may now consider some of the digital peculiari- 

 ties whose inheritance has been studied in man. 

 A very good case is that of split hand and foot, or 

 " lobster claw." Lewis and Embleton (1908) consider 

 a collection of 180 cases of this deformity. They find 

 it by no means uncommon. Many varieties of the 

 condition occur. In the " G " family, to which many 

 of their data refer, the hands are variously misshapen, 

 and each foot consists of two toes separated by a 

 deep cleft. Rarely the toe on one side may be double, 

 and the toes are generally bent claw-wise at their 

 extremities. Both the hands and feet of these people 

 are said to have great functional capacity and 

 accuracy in use, including needlework and hand- 

 writing. The variations in the deformity are only 

 in degree. Rarely one or both hands ma}^ be normal 

 when the feet are split. The condition may also be 

 associated with syndactyly (fused fingers) or Poly- 

 dactyly (extra fingers or toes). Cross bones frequently 

 occur in the hands, but never in the feet. The in- 

 heritance is essentially that of a Mendelian domi- 

 nant, though the expected ratios are not always 

 adhered to. 



In the " G " family this condition has been traced 

 through five generations. It never skips a generation. 



