482 CHARLES R. STOCKARD AND E. M. VICARI 



dividual, and the time and effort necessary to do so would 

 scarcely seem worth while. It is felt that if the parathyroid 

 glands play a type-determining role in differentiating the 

 several contrasted breeds of dogs, a fair sample of the glands 

 from any well expressed type should show indications of 

 the modified function as well as any other sample or possibly 

 even all the parathyroid bodies from the given individual. 



Figures 4, 5 and 6 in plate 91 illustrate sections of the 

 parathyroids from three second generation Boston terrier- 

 dachshund hybrids. In this generation there is wide varia- 

 tion in general body form and type, and unique specimens 

 may appear, the characteristics from the two parent stocks 

 being strangely mixed and combined in one individual. As 

 discussed previously, the thyroid and pituitary glands also 

 differ very widely in their histologic patterns in these F 2 

 hybrids. 



Figure 4 illustrates a section through a small parathyroid 

 body lying within a compartment of the same connective 

 tissue coat which surrounded a large cyst. This cyst was 

 lined with embryonic branchial epithelium ciliated over most 

 parts, and was filled with a lightly staining fluid containing 

 sparsely scattered cells. There is no doubt that the lining 

 of this cyst is a remnant of branchial epithelium which 

 normally should have differentiated into parathyroid or 

 thyroid tissue in this region. Smaller cysts of similar type 

 are frequently found within the parathyroid bodies, and are 

 indicative of arrests and inhibitions in the outgrowths of 

 branchial epithelium designed to form the endocrinic glands 

 which arise from the branchial pouches of the embryo. We 

 have already seen in the pure Boston terrier and these 

 Boston terrier-dachshund hybrids that embryonic arrests in 



PLATE 91 



EXPLANATION OF FIGURES 



Boston terrier-dachshund cross. Histologic nature of the parathyroid glands 

 in the pure breeds and their first and second generation hybrids. 



1 Dachshund 255 $>. 3 F, 127 <j>. 5 F 3 354 $>. 



2 Boston terrier 536 $>. 4 F 2 781 <j>. 6 F 2 355 $. 



