PARATHYROIDS 



487 



Parathyroids. There are smaller glandular structures associated 

 with the thyroids on each side known as the parathyroids. One is located 

 at the level of the lower border of the cricoid cartilage and in intimate rela- 

 tion to the posterior border of the lateral lobe of the thyroid. The other is 

 at the inferior border of the same lobe. In the dog there is an anterior para- 

 thyroid at the head of the thyroid and an external imbedded in the mass of 

 the thyroid. Their structure is somewhat different from that of the thyroid, 

 and it has been claimed that after the removal of the thyroid, the parathyroid 

 tissue develops a structure more nearly comparable to the thyroid. The 

 parathyroids bear a close relation anatomically and physiologically to the 

 thyroids. It is still the view that the parathyroids are intimately associated 

 with the thyroids in the construction of the thyroid compound, and Mendel 

 has found iodine in the parathyroids. This supports the view that the para- 



Epith. c. 



on. tis. 



Coll. 



A 



Epith. c- 



Epith. c.-l 



->.- 



Thy. 



Ves. 



'Coll. 

 Bid. t. 



-Ves. 

 Conn. I 



Coll. 



FIG. 313. Normal parathyroid tissue of 

 the cat. (Vincent and Jolly.) 



FIG. 314. Parathyroid of the cat 

 after the thyroids have been removed, 

 showing enlarged vesicles with colloid. 

 (Vincent and Jolly.) 



thyroids prepare the iodine compound which is later stored in the thyroid. 

 A supplementary view by Koch is presented later. 



a. Parathyroidectomy. The removal of the parathyroids is more dis- 

 turbing, on dogs at any rate, than the removal of the thyroids. Dogs survive 

 the operation only a short time, three to five days. They show deranged 

 metabolism and quickly develop a characteristic disturbance of nerve 

 muscular control to which the name of tetany has been applied. Restless- 

 ness, excitability, muscular tremors which in the later period pass into mild 

 convulsions, with tetanic rigor and exhaustion, followed by death is the cycle 

 of events after this operation. It has also been shown that the removal of the 

 parathyroids in the dog leads to an increased excretion of calcium and of 

 ammonia and of other products indicative of disturbed metabolism. The 



