110 CHARLES R. STOCKARD 



and not so twisted. The radius and ulna of the bassethound- 

 Naluki leg are not as thickened nor so gnarled with exostoses 

 as in the other three. This is the only one of the four leg' 

 skeletons in which the distal process of the ulna projects 

 slightly beyond the end of the radius, and the foot in this F. 2 

 bassethound-Saluki is less abducted than in the other F., 

 skeletons. 



The F 2 bassethound-shepherd, the second skeleton in figure 

 3, shows the pure achondroplasic reaction on shepherd typed 

 bone. The bones in this leg are thicker in proportion to 

 length than in the first leg of this group, and the scapula is 

 very wide for its length. The ulna does not extend below 

 the radius and the wrist is free to rotate and abduct the fore- 

 foot. The first two leg skeletons in this figure are both longer 

 than the pure bassethound leg seen at the right end. 



The third skeleton of figure 3 is from an F 2 bassethound- 

 bulldog. It is as completely achondroplasic in shortness and 

 form as that of the pure bassethound at its right. These 

 two leg skeletons are bone for bone almost exactly alike. The 

 ulna falls short of the radius in its lower extent, thus ren- 

 dering the wrist joint very unstable, and the foot is badly 

 abducted. The excessive shortness of bones in the legs of 

 the Fo group homozygous for achondroplasia is appreciated 

 more clearly by comparing them with the leg skeletons from 

 the heterozygous F,s (fig. 2, pi. 23). Comparisons made among 

 the several leg skeletons in each of these groups make it 

 clearly evident that the influence of the dominant gene for 

 achondroplasia of the extremities differs, depending upon the 

 breed constitution of the animal involved. The functioning 

 of the same gene gives different results when acting upon 

 different constitutions. Among these breeds of dogs the 

 Saluki constitution is the most resistant to the effects of the 

 gene for short achondroplasic legs and the bulldog bone is 

 the most responsive. The hound typed bone of the bassethound 

 itself is probably not so responsive as that of the bulldog, 

 and on this account a heterozygous F 2 bassethound-bulldog 

 with bull typed bone may be equally as low and short legged 



