16 CHARLES R. STOCK ARD 



the elbow almost shoulder high, a condition caused by the 

 spiral twist in the long bones affecting the plane of flexion 

 of the elbow joint. There is thus a generous, wide movement 

 in bringing the hand to the mouth. 



Many weird explanations of the causes of achondroplasia 

 have been offered in a serious scientific manner. One of the 

 most fantastic of these attributed the clear-cut modified his- 

 togenesis of achondroplasia in both cranium and extremities 

 to the influence of amniotic pressure on the developing fetus. 

 This thesis, with beautiful illustrations, was presented by 

 Murk Jansen ('12), a Dutch orthopaedic surgeon, and the 

 late Sir G. Elliot Smith, the British anatomist, wrote an 

 introduction of strong approval. In the light of our in- 

 vestigations on the genetics and development of this condition 

 in dogs, as well as the studies of Landauer on fowls and of 

 Knotzke ('29) on the morphology and histology of this dis- 

 torted bone growth, such explanations of the histologic proc- 

 esses involved are altogether untenable. 



Achondroplasia, or chondrodystrophy, the deficient growth 

 of bones derived from a cartilage matrix, may, in a certain 

 sense, be interpreted as an opposite reaction to that of gi- 

 gantism or acromegalic overgrowth of bone. As in acro- 

 megaly, much evidence for a strong correlation between the 

 dwarf growth reactions and modifications of the pituitary 

 gland is found. In these dwarf cases one would expect the 

 pituitary deviations to differ from or even directly oppose 

 those associated with the giant growths. If modifications of 

 the pituitary are the causative elements in both the giant and 

 the dwarf growth deviations, one would assume the glandular 

 abnormality associated with overgrowth or acromegaly to be 

 a contrasted and opposite condition to that associated with 

 the deficient dwarf growths. Yet as a result of hybridizing 

 certain dog breeds, we have been faced with a very remarkable 

 situation in which achondroplasic dwarfing in certain parts 

 and acromegalic overgrowth in other parts are produced in 

 one and the same individual. 



