504 



E. V. COWDRY 



rats, and in this respect resemble the suprarenals and hypophysis (Jack- 

 son). The same author has also found that in the white rat their growth 

 energy exceeds that of the thyroid; for in young white rats, held at main- 



Fig. 4. Lateral lobe of the thyroid 

 gland with included parathyroid (p) of 

 normal white rat, after Jackson. 



Fig. 5. Lateral lobe of the thyroid 

 gland with included parathyroid of young 

 white rat held at maintenance of body 

 weight by underfeeding, after Jackson. 



tenance of body weight through underfeeding for three weeks, the para- 

 thyroids actually continued to grow and increase in size, while the amount 

 of thyroid tissue suffered a marked reduction. Compare Figs. 4 and 5. 



Comparative Anatomy 



Comparative anatomy sheds no light upon our understanding of the 

 parathyroid glands. With the exception of the fishes,, they are represented 

 in all the classes of vertebrates, and everywhere are characterized by their 

 extreme variability. Their variation in structure in the different domes- 

 tic animals is discussed by Vermeulen. A study of the parathyroid body 

 weight ratio in different classes of animals is much needed. 



Histology 



Histologic Morphology. The parathyroids possess a capsule of fibrous 

 connective'tissue. The glandular cells within the capsule are disposed in 



