Anatomy, Embryology, Comparative 



Anatomy and Histology of 



the Parathyroids 



E. V. COWDKY 



NEW YORK 



Anatomy 



Gross Morphology and Relations. The parathyroid glands are small 

 bean shaped structures about six millimeters long, three millimeters broad, 

 and two millimeters thick, weighing 

 in all about fifty-five centigrams, but 

 so great is the variation that no two 

 investigators ever give the same fig- 

 ures. Their number is variable, 

 ranging from four to five or six, or 

 as many as eight. Usually they are 

 found in two pairs, superior and 

 inferior. 



The superior parathyroids are 

 thought to be rather more constant in 

 position. They occur on the medial 

 aspect of the dorsal surface of each 

 lateral lobe of the thyroid gland, at 

 about the junction of its upper and 

 middle thirds (Fig. 1). Sometimes 

 they are embedded in the substance 

 of the gland in lower forms, but in 

 man they are usually separated from 

 it by the thyroid capsule. Never- 

 theless, they are often called "in- 

 ternal," as contrasted with the in- 

 ferior or "external" glands. 



The inferior parathyroid glands 



likewise occur on the dorsal surface of each lateral lobe of the thyroid 

 gland, but further caudad. They are occasionally associated with the 



501 



Fig. 1. Dorsal view of 

 ra 

 alsted and vans. 



parathyroid glands from 



thyroid and 

 Lewis, after 



