GENETIC TYPE AXD THE EXDOCRINES 343 



did the mutations in the bulldog-. This may represent an 

 additional step in the mutational series bringing about the 

 flat face. Prognathism of the mandible is only mildly ex- 

 pressed in the F 2 Brussels griffon-dachshunds and is in con- 

 trast to the long, protruding and up-curved mandible in the 

 bulldog and the bulldog-bassethound hybrids. In this cross 

 the head forms are again found to be expressed as a complex 

 of characters influenced in their development by a number 

 of genetic factors. Some of the mutant or modified factors 

 are dominant and others recessive to the determiners for 

 normal form. 



The Fj Brussels griffon-dachshund was backcrossed with 

 the dachshund parent, and eight hybrids were whelped. These, 

 as would be expected, were quite dachshund-like in cpiality. 

 All had long muzzles, some of which were almost typically 

 dachshund, and others showed a considerable depression at 

 the nasion as a last character from the Brussels griffon. All 

 were short legged, and about half the individuals had long 

 hair, in some cases rough and in others silky. Plate 33 (p. 136) 

 illustrates five of these backcross dachshund hybrids. 



The Head Features ix Dachshund-Pekingese Hybrids 



In the Asiatic Pekingese dog the reduced muzzle projects 

 very little if at all beyond the overhang of the bulging fore- 

 head. This pattern of growth is quite definitely the result 

 of achondroplasia in the basicranium and the facial skeleton, 

 similar in kind to the growth disturbances giving form to 

 the bulldog head. The high bred Pekingese, with its wide, 

 fiat face, large, protruding grape-like eyes, snoring pug nose 

 and tight, snappy mouth can scarcely be claimed to have 

 arisen from the same ancestral stock giving origin to the 

 bulldog breeds in Europe. It seems logical to imagine that 

 an Asiatic dog resembling the chow was the ancestral fore- 

 runner from which a mutation or series of mutations brought 

 about the development of the achondroplasic dwarf Pekingese 

 dog. The bodily characteristics of this achondroplasic sport 



