116 CHARLES R. STOCKARD 



On this constitutional basis, a comparison of the leg skele- 

 tons of F 2 bassethound-shepherd hybrids in plate 24 and the 

 F 2 bassethound-Salukis shown in plate 25, clearly demon- 

 strates well marked differences in the degree of response 

 to the achondroplasic factors in the two combinations of 

 breed types. There is no doubt that Saluki bone is much 

 less responsive to the factor for achondroplasia in the leg 

 than are the shepherd and the hound bone types. 



Plate 26 illustrates the comparative effects of one gene 

 or two genes for achondroplasia of the legs. The first skeleton 

 is from F 2 1440 6 , which was shown as the third leg skeleton 

 in plate 25. This leg was diagnosed as heterozygous, si, 

 having but a single gene for achondroplasia, on Saluki typed 

 bone. The second skeleton is from F x 504 6 and must of 

 necessity be heterozygous, si, for the short factor. The two 

 photographs show these skeletons to be almost exactly alike, 

 the only slight difference being that the F 2 leg may be some- 

 what more nearly complete for Saluki bone than the F 1? as 

 indicated by its slenderer form. In both skeletons the distal 

 end of the ulna projects below the articular surface of the 

 radius and obstructs carpal rotation and excessive abduction 

 of the foot. The state of this arrangement is a reliable index 

 of the degree of achondroplasic deformity. 



The third leg skeleton in plate 26 differs greatly from the 

 other two. The F 2 animal, 1211 $ , from which this leg skeleton 

 was taken, had been clearly recognized in life as having the 

 most extreme degree of leg shortness to be found among 

 basscthound-Saluki hybrids. This dog, which had slightly 

 long hair, is photographed from life in plate 12 (right in 

 fig. 1) and is standing beside a short haired brother whose 

 more purely developed Saluki typed bone was evident even 

 in life. No. 1211 $ was classed as homozygous or 8.9 for 

 achondroplasia and the leg skeleton illustrates how much this 

 defect is accentuated when pure ss, instead of the mixed or 

 single si genie condition for short leg, reacts on this type 

 bone. The distal end of the ulna in this skeleton falls short 

 of the end of the radius and offers no obstruction to outward 



