THE CONTRASTED PATTERNS AND MODIFICATIONS OF 



HEAD TYPES AND FORMS IN THE PURE BREEDS OF 



DOGS AND THEIR HYBRIDS AS THE RESULTS OF 



GENETIC AND ENDOCRINIC REACTIONS 



THE PROBLEMS INVOLVED IN THE STUDY OF HEAD TYPES 



AMONG DOGS 



In the preceding chapters we have considered the widely 

 contrasted differences in structural growths and arrange- 

 ments found in the extremities of the pure dog breeds. Most 

 pronounced deviations from the ancestral or wild type occur 

 as strictly localized deformities in leg length and shape, while 

 all other parts of the animal are perfectly normal in their 

 expression. The present chapter will deal with the heads and 

 underlying skull structures among the different dog breeds 

 which we shall find are as strongly modified and contrasted 

 as are the extremity types. However, the head involves a 

 greater number of features and is much more complex than 

 the extremities, and necessitates the calculation of indices 

 for comparisons. In some breeds we again find that the head 

 distortions are a strictly localized modification in an animal 

 with otherwise normal structural arrangements. The King 

 Charles spaniel and the Brussels griffon, though midget 

 dwarfs in size, are well formed and normally proportioned 

 in all regions of the body with the exception of their skulls, 

 which deviate enormously from the wild dog pattern. The 

 English bulldog, French bulldog and Boston terrier show 

 highly modified conditions of the skull as a growth complex 

 quite independent of the less pronounced modifications oc- 

 curring in other regions of the body. 



The skull modifications in certain breeds are accompanied 

 by characteristic arrangements of teeth which differ from 

 those of the standard shepherd. Moreover, there are consti- 



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