476 CHABLES B. STOCKABD AND E. M. VICABI 



to the peculiar types concerned. It will be recalled from 

 previous chapters on skull types and leg lengths that the 

 bone growth from endochondral and epiphyseal plate ossi- 

 fication may be much retarded in localized regions, as for 

 example the basicranium and caudal vertebrae, while the 

 increments in other regions with the same manner of growth, 

 as well as growth from subperiosteal and membrane bone 

 ossification, are little or not at all affected in an adverse 

 manner, and may even be accelerated. Such differences in 

 growth expression between localized regions of endochondral 

 ossification in the same body have not been obtained by the 

 experimental removal of endocrine glands, which gives gen- 

 eral reactions that are equally evident in all the regions of 

 the body where similar types of growth occur. These results 

 from surgical methods have given rise to the widely accepted 

 interpretation that modifications in form and quality of 

 growth may result solely from endocrinic disturbance. How- 

 ever, the sharply localized distortions of endochondral and 

 epiphyseal bone growth so decidedly expressed in several 

 dog breeds do not lend themselves to this simple interpreta- 

 tion. In fact, in order to understand these localized reactions, 

 we are forced to study not only the genetics of such char- 

 acteristics, but also the different stages of susceptibility to 

 developmental distortions and the possibility of temporary 

 arrests and disturbances in early endocrinic functions which 

 later may be completely repaired. The present consideration 

 deals with the question of whether the histology of the para- 

 thyroid glands from adult Boston terrier-dachshund hybrids 

 shows indications of such early developmental arrests and 

 disturbances. 



Before entering into the discussion of differences in micro- 

 scopic structure among the parathyroids from the pure 

 breeds and their hybrids, several general facts regarding 

 them must be presented. To begin with, the number and size 

 of the parathyroid bodies in the dog are quite variable. These 

 bodies also vary in topographic relations and intimacy of 



