389 



The Thyroid and Parathyroid Glands throughout Vertebrates. 



By F. D. Thompson. 



(Communicated by Prof. E. A. Schiifer, F.E.S. Received December 29, 1909, — 



Read February 3, 1910.) 



(Abstract.) 



1. The organs recognised as arising in the regions of the gill-clefts in 

 Elasmobranchs are thyroid, thymus, and post-branchial body. The para- 

 thyroid and carotid glandules have not yet been discovered in these animals. 



2. Within the thyroid gland of Elasmobranchs are small, solid masses of 

 cells, partly epithelial, partly adenoid. These have not, so far as I am 

 aware, been previously described. One is tempted to suppose that these are 

 homologous either with parathyroid or thymus. In the latter case it would 

 correspond with thymus IV of Mammals. (It has not been suggested that 

 the thymus derivative of the fourth cleft furnishes isolated nodules in the 

 thyroid of Elasmobranchs.) 



3. In Teleosts the only organs of the series are the thyroid and the thymus. 

 The parathyroid has never been described in this group, and it is doubtful 

 whether there is any trace of post-branchial body. The thyroid in Amiurus 

 consists of a few scattered vesicles embedded in the connective tissue matrix. 

 The cells lining the vesicles are very low columnar, and in some cases almost 

 flat. 



4. In Urodela the branchial cleft organs are thyroid, thymus, parathyroid, 

 and post-branchial body. The thyroid is fairly superficial, and there is no 

 intimate relation with the parathyroid. 



5. In Anura the branchial organs are, in addition to thyroid and parathyroid, 

 thymus, post-branchial body, ventral " Kiemenreste " and carotid gland. 

 The thyroid is very small and deeply placed. The parathyroid has not yet 

 entered into intimate relations with the thyroid. The ventral " Kiemenrest " 

 is a large striking-looking organ which must have been frequently mistaken 

 for the thyroid, and appears to be a hsemolymph organ. The arrangement of 

 the cells in the parathyroid is somewhat characteristic, and is described in 

 the text. 



6. In Reptiles, thyroids and parathyroids are still anatomically separate 

 organs, but the parathyroid in some instances possesses distinct lumina, and 

 in this the fundamental distinction between thyroid and parathyroid is at 

 once broken down. Moreover, in this group there are clear indications that 

 the post-branchial body secretes colloid. 



VOL. LXXXII. — B. 2 I 



