244 CHARLES E. STOCKARD AND A. L. JOHNSOX 



the fully concave dachshund condition. The character be- 

 haves as a typical single factor recessive, although in the 

 heterozygous condition it is not completely suppressed and 

 the convex pattern of the condyle is somewhat flattened. 



In plate 41 the differences in the degree of divergence of 

 the mandibular rami in the dachshund and Boston terrier 

 are readily noticeable. This divergence is again uniformly 

 intermediate in the Fj hybrid while the F2 hybrids present 

 various degrees of divergence. The F 2 mandible in figure 4 

 shows a wide degree of divergence, as found in the Boston 

 terrier, and associated with this condition is the concave 

 condyle typical of the dachshund. This association indicates 

 that the concave condyle of the dachshund is not genetically 

 related or linked with the general form of the dachshund 

 mandible. 



The backer osses of the F^ hybrid Boston terrier-dachshund 

 on the two pure stocks. Backcrossing the F : hybrid on the 

 Boston terrier parent stock tends to give some quite well 

 expressed Boston terrier heads in combination with various 

 characters from the two stocks. Plate 43 illustrates the two 

 parent stocks (figs. 1 and 2) and an F! male (fig. 3). Breeding 

 such a male back to the Boston terrier female produced the 

 hybrid photographed as a mounted specimen in figures 4 

 and 5. This backcross hybrid exhibits several peculiar com- 

 binations of characters from the two stocks. In the first 

 place, the head is fairly typical of the Boston terrier. The 

 ears are held in the erect Boston terrier position in spite of 

 the fact that they are very large and long, a characteristic 



PLATE 43 



EXPLANATION OP FIGURES 



Backcross of the Fj dachshund-Boston terrier with the pure Boston terrier 

 showing recombinations of characters of the two pure stocks. 



1 Boston terrier 435 $. 



2 Dachshund 255 $. 



3 F, 128 <?. 



4-5 Backcross 634 . Note the long dachshund-like ears carried in the erect 

 Boston terrier position, and the short achondroplasic legs of the dachshund in 

 combination with the short, bent tail and coat markings of the Boston terrier 

 breed (see also fig. 4, pi. 44). 



