GENETIC TYPE AND THE ENDOCRINES 17 



Not only do we obtain peculiar mixtures of growth reac- 

 tions on crossing different breed types, but modified struc- 

 tural responses are sometimes localized or limited to certain 

 narrow regions, while other parts of the animal conform to 

 the usual or normal pattern. Extreme structural dishar- 

 monies as well as minor disharmonious relations among 

 structures and functions are frequently found to occur in 

 hybrids. 



Many of the pure-line dog breeds are in themselves char- 

 acterized by localized deformities. The dachshund and basset- 

 hound, for example, are quite normal in body and head form, 

 having perfectly normal axial skeletons with long tails, but 

 their extremities show exaggerated achondroplasia and are 

 twisted and much reduced in length. On the other hand, the 

 King Charles spaniel, Boston terrier, Brussels griffon and 

 several other breeds have quite normally developed long, 

 straight legs, while the head, and in some cases both head 

 and tail, exhibit extreme shortness and distortion due to 

 achondroplasia of the basicranium and jaws and, in those 

 in which the tail is also involved, of the caudal vertebrae. 

 Localized growth distortions of closely similar nature also 

 occur among human beings. Certain individuals with quite 

 normally proportioned heads and bodies may have dispro- 

 portionately short, twisted arms and lower extremities; these 

 might be classed as human bassethound or dachshund types. 

 Again, there are persons with long, straight extremities who 

 show a much flattened face with depressed, sunken nasion, 

 short maxillary region and protruding lower jaw — a bulldog- 

 faced man. Sharply localized overgrowths, such as excessive 

 thickening and wrinkling of the skin in the head and shoulder 

 regions, also occur in human individuals. 



All these localized peculiarities and mixtures of type make 

 it difficult to credit a specific endocrine disturbance as the 

 sole causative agent for any one of them, since the same 

 endocrine secretions necessarily surround, and are in contact 

 with all parts of the body. The nature of the localized or 

 specific tissues themselves — their genetic constitutions — must 



