126 CHARLES R. STOCKAED 



while the axial skeleton — the skull and vertebral column — 

 shows no indication of achondroplasic defects. The head is 

 well formed with a long slender muzzle and the tail is long 

 and normally motile. As in most hound breeds, the ears are 

 long and pendulous and the skin moderately loose. The 

 dachshund weighs less than half as much as a normal sized 

 hound. This dog is thus an ideal animal for the investigation 

 of the origin and development of chondro dystrophic ex- 

 tremities. 



The Boston terrier breed is highly contrasted in type 

 with the dachshund except that it also is a dwarf. The legs 

 of this animal are long and perfectly straight. The head 

 and tail are bulldog-like in pattern, which is due to a decided 

 chondrodystrophic reaction at both ends of the axial skeleton 

 (a characteristic to be considered in a later section of this 

 study). The defective growth of cartilage and bone is sharply 

 localized in the skull and caudal end of the vertebral column ; 

 the bones of the extremities grow in a perfectly normal 

 manner. At this time we shall limit our consideration entirely 

 to the contrasted extremities of the Boston terrier and the 

 dachshund. 



Tn our cross matings between dachshunds and Boston ter- 

 riers, members of both breeds have been used as sires and 

 dams. The F x offspring from the dachshund mother and the 

 Boston terrier father are indistinguishable from those with 

 a Boston terrier dam and a dachshund sire. All members 

 of the first hybrid generation have short achondroplasic legs, 

 never the long straight legs of the Boston terrier parent. 

 The short legs of the dachshund are dominant when crossed 

 on long legged stock just as are those of the bassethound, 

 and again the legs of the F 1 animal are not so short nor 

 completely achondroplasic as those of the short legged parent. 

 The heterozygous si condition gives an intermediate length 

 to the Fj leg. Plate 29 shows photographs of the dachshund 

 (fig. 1) and Boston terrier (fig. 2), with their extreme con- 

 trast in leg length. The two ¥ r animals in figures 3 and 4 

 are dachshuud-Boston terriers and the three in figure 5 are 



