424 CHARLES R. STOCKAHD AXD E. M. VICAR1 



comparisons between the more highly modified breeds and 

 the more nearly normal types and emphasizes the wide dif- 

 ferences in thyroid structural quality and arrangements. 



Those familiar with the histology of the thyroid gland 

 will appreciate how practically impossible it is to select for 

 a photomicrograph a single small spot which will fairly rep- 

 resent all the peculiar characteristics that might occur 

 throughout the gland. The follicles are very rarely of equal 

 size and of uniform distribution; neither are the supporting, 

 vascular and other interfollicnlar tissues uniformly arranged 

 in the different areas. The superficial and central portions 

 of the gland usually differ considerably for follicular size 

 and relative proportions of parenchyma to other tissues. In 

 spite of regional variations which are common to all thyroid 

 glands, it is possible, with the material under consideration, 

 to select areas for photomicrographs which show particular 

 patterns of thyroid structure that are more or less typically 

 characteristic in a given breed of dogs. 



In the discussion of the glands, definite effort will be made 

 to bring out further points of importance that cannot be 

 recognized from the photographs in the plates. Space pro- 

 hibits, however, an unlimited treatment of all the details, 

 many of which are without known significance. We shall 

 discuss the structures with as much discrimination as is 

 feasible. 



The German shepherd and foxhound are normal or standard 

 typed dogs, and the histologic structure of their thyroid 

 glands furnishes a very satisfactory control pattern. Figure 



PLATE 81 



EXPLANATION OF FIGURES 



Photomicrographs of typical sections of the thyroid glands from two short 

 muzzled breeds (the English and French bulldogs) and two long muzzled breeds 

 (the bassethound and foxhound). The contrast in histologic patterns between 

 the two types is strongly marked. 



1 English bulldog 119^. 



2 French bulldog 109$. 



3 Bassethound 277 $. 



4 Foxhound 90 $. 



