GENETIC TYPE AND THE ENDOCRINES 337 



THE HEAD FEATURES IN BRUSSELS GRIFFON-DACHSHUND 



HYBRIDS 



Two midget Brussels griffon males of the best breed lines 

 were crossed with two pedigreed dachshund females. The 

 extreme contrast between the flat monkey-like face of the 

 griffon and the long slender muzzle of the dachshund is 

 clearly shown in figures 1 and 2 of plates 33 (p. 136) and 

 64. The long straight legs of the griffon are also sharply 

 contrasted with the short achondroplasic legs of the dachs- 

 hund. The genetics of leg length in this cross has been pre- 

 sented in an earlier section. 



Achondroplasia of the extremities is transmitted as a single 

 factor dominant character completely independent of the 

 factors determining the flat face or the long muzzle. Among 

 the second generation hybrids the shortened muzzle may 

 appear in association with either the long or short legs, just 

 as was the case among the bulldog-bassethound hybrids. 



Figures 3-6 in plate 64 illustrate the first generation, F 1; 

 dachshund-Brussels griffon hybrids. They all show the domi- 

 nant short leg of the dachshund and the long, rough hair of 

 the griffon. The muzzle is considerably shorter than that of 

 the dachshund and the depression at the nasion, the "stop," 

 is much more pronounced. Yet in comparison with the head 

 of the Brussels griffon, the F t muzzle is very long and the 

 jaws very strong. 



The mandible in the F x is not always so much shortened 

 as is the maxilla. Among ten specimens of this generation, 

 six showed prognathism of the mandible, "undershot" mal- 

 occlusion, and one female had opposition of the incisors rather 

 than the proper occlusion with lower incisors fitting behind 

 the upper. This again emphasizes the fact that the abbrevia- 

 tion of the face in the short headed deformity is due to a 

 complex of genetic influences, some dominant and some re- 

 cessive, and all quite independent of one another, so that 

 different parts are not always affected in a corresponding 

 manner in a given individual. Structural disharmonies with 



