INANITION OF THYROID IIST RATS 335 



THE PARATHYROID GLAXD 



The normal structure of the parathyroid glands will be con- 

 sidered first, followed by a discussion of the changes produced 

 during inanition, 



a. XoDiial structiirc of the parathyroid gJdnds 



As is well known, there is in the rat a single paii- of i^arathyroid 

 glands, said to correspond to parathyroid III. In onc^ excep- 

 tional case, I found a parathyroid (see table 1 ) on one side only. 

 I have never observetl the accessory parathyroids described by 

 Erdheim (cited by Biedl '13). The parathyroids are located upon 

 the external surface of each lateral lobe of the thyroid gland, 

 usually somewhat posteriorly, though occasionally moi'e anteri- 

 orly (figs. 1, 3, 4, 5, 6). 



Ochsner and Thompson ('10) state that the parathyroids of 

 the rat are located within the thyroid lobes near the upper pol(\ 



1 find, however, that there is considerable variation; they occur 

 slightly more frequently opposite the middle third of the thy- 

 roid lobe, but often at more cephalic or caudal levels. Of 59 

 glands whose position was noted, 18 were located in the cephalic 

 third of the thyroid, 20 in the middle third, 13 in the caudal 

 third, G at the junction of the cephalic and middle thii'ds, and 



2 at the junction of middle and caudal thirds. The parathyroids 

 of the two sides are usually, but not always, at nearly the same 

 level. In 3 cases observed, one parathyroid was located in the 

 cephalic third of the lateral lobe of the thyroid, while the oppo- 

 site parathyroid corresponded to the caudal third of the thyroid. 



The parathyroid gland lies partly embedded within the thy- 

 roid, about one-fourth to one-third of its surface usually forming 

 an external free or exposed surface (figs. 1, 3, 4, 5, 6). Sometimes 

 it may project more extensively from the thyroid surface; in 

 other cases it lies more deeply, rarely entirely embedded within 

 the thyroid. 



As to size, the dimensions of the parathyroid gland at vari- 

 ous ages are given in the following table. 



