240 CHARLES R. STOCKARD AND A. L. JOHNSON 



plate 37 shows the mandibles arranged in the same manner 

 as the skulls. We have called attention before to the char- 

 acteristics of the two parent types. In the F x hybrids the 

 skulls are very closely alike, as should be the case when 

 two parent stocks are homozygous or pure for their skull 

 types. The Fj skull and lower jaw are seen to be a combina- 

 tion of the two parental types, the total complex for neither 

 type being completely dominant. Certain elements of the 

 skull of the Boston terrier, such as the strongly curved arch 

 of the zygoma and the depression at the nasion, may be found 

 in combination with the long facial skeleton and strong denti- 

 tion of the dachshund. Evidently all these different features 

 are transmitted in a somewhat independent fashion; they 

 are certainly, at least, expressed in such a manner. 



Figures 4, 5 and 6 in these two plates illustrate the skulls 

 and mandibles of three litter mates in the second hybrid 

 generation. These skulls show various recombinations of the 

 features derived from the two parent types. Figure 4 ap- 

 proaches somewhat nearer the dachshund type than does the 

 Fj skull, yet the approach is by no means complete. Figure 5 

 has more the features of the Boston terrier and has also 

 extremely defective dentition and malformed teeth with hypo- 

 plasia of the enamel. Figure 6 could almost be that of a 

 Boston terrier with imperfect facial type. In rather rare 

 cases the pure bred Boston terriers may diverge from type 

 to as great an extent as does this last skull. 



In text-figure 56 (figs. 4 and 5) the sagittal outlines of 

 two of these highly different F 2 skulls are superimposed 



PLATE 41 



EXPLANATION OP FIGURES 



Ventral view of the mandibles of the dachshund, Boston terrier and their first 

 and second generation hybrids showing concave articular surface of the condyles 

 in the dachshund as opposed to the convex surface in the Boston terrier, and the 

 expression of this character in the hybrids. The difference in the degree of 

 divergence of the mandibular rami in these two breeds and its expression in the 

 hybrids is also clearly shown. 



1 Dachshund 255$. 2 Boston terrier 536$. 3 F, 130$. 

 4 F 2 722^. 5 F 2 1522^. 6 F 2 781 $. 7 F 2 810 <?. 



