ACHONDROPLASIA OP THE EXTREMITIES; A DEFINITELY 

 LOCALIZED AND HIGHLY ALTERED GROWTH REACTION 



The careful study of the genetics and development of a 

 strongly expressed but sharply localized alteration in growth 

 would seem to be the simplest mode of approach to our general 

 problem of the interrelation of the genetic constitution of the 

 tissues and the endocrinic influences in determining struc- 

 tural quality and form. The extremely short and deformed 

 legs of the dachshund and the bassethound breeds offer the 

 most clear cut examples of the condition desired. The modi- 

 tied legs in these dogs arc found to result from a typically 

 achondroplasic growth reaction. The epiphyseal growth 

 cartilages in the extremities fail to give the usual longitudinal 

 proliferation of cartilage cells as forerunners for the normal 

 growth in length of the long bones. Instead, the cartilage 

 is abnormally scant and the cellular proliferation and growth 

 take place in transversely spiral and other irregular direc- 

 tions, exactly as has been frequently reported for human 

 achondroplasia and is clearly illustrated and discussed by 

 Knotzke ('29). This chondrodystrophy and modification of 

 subperiosteal bone formation are exactly the kinds of growth 

 distortions thought to result from diseased or defective con- 

 ditions of the endocrine system, and particularly of the 

 pituitary. They are commonly treated clinically from this 

 standpoint. 



The fact of extreme importance in connection witli the 

 dachshund and bassethound breeds is the sharp limitation of 

 chondrodystrophy to the skeleton of the extremities, while 

 the axial skeleton — the skull and vertebral column — completely 

 escapes. If abnormal endocrine secretion is the causative 

 agent in producing this skeletal deformation, why should one 

 part of the skeleton suffer and other parts completely escape, 

 while all parts are necessarily exposed to the influences of 



