GENETIC TYPE AND THE ENDOCRINES 477 



contact with the thyroid gland. Usually two or more para- 

 thyroid bodies are found on each side, one closely attached 

 to the mid-dorsal surface of the thyroid and the other located 

 in the loose fascia at or near its anterior tip. Accessory 

 parathyroids are frequently present in irregular positions. 

 For convenience, those bodies lying about the thyroid may 

 be designated as " external" parathyroids, since, in addi- 

 tion to these, one or more discreet masses of parathyroid 

 tissue may lie within the connective tissue capsule or be 

 completely buried within the tissues of the thyroid gland 

 itself. These will be designated as "internal" parathyroids. 



The parathyroid bodies are oval in outline and compara- 

 tively thin dorso-ventrally. They differ greatly in size, rang- 

 ing from tiny particles of only one millimeter in length to 

 fairly large masses almost one centimeter long. The external 

 parathyroids are usually larger than those buried within the 

 thyroid capsule, yet the internal parathyroids are often of 

 considerable size. The size of parathyroid bodies varies in 

 general with the size of the dog; they are very large in the 

 St. Bernard and great Dane dogs and quite minute in the 

 dwarf, midget and toy dogs. The parathyroid bodies in the 

 bulldogs and St. Bernards are usually somewhat thicker 

 dorso-ventrally, giving a plumper appearance than those in 

 the long muzzled and more normal breeds. Since there are 

 a number of distinct external and internal parathyroid bodies 

 connected with the thyroid gland, it has not seemed practical 

 to attempt estimates of the relative amounts of parathyroid 

 tissue per unit of body weight for the different breeds, as 

 was done for the thyroid and pituitary glands. 



Histologically, the parathyroid is much more homogeneous 

 than either the thyroid or the pituitary. In its normal state 

 it is a uniform compact mass of epithelial cells that have 

 a definite tendency toward irregular cord-like arrangements; 

 the parathyroids are very vascular and have a sparse amount 

 of connective tissue. Almost all the cells of the human para- 

 thyroid gland, and likewise of the dog parathyroid, are of 



