THE THYROID AND PARATHYROIDS 259 



has naturally led to much confusion, owing to the fact that 

 the same term has been sometimes applied to the true acces- 

 sory thyroids. The matter was finally made clear by Maurer, 

 who recognized the homology of these organs with the glan- 

 dulse parathyroidese which were discovered in higher animals 

 by Sandstrom in 1880, and independently by Baber, Horsley, 

 and Gley. 



The parathyroids of the frog are represented on either 

 side of the body by two oval or spheroidal corpuscles placed 

 one behind the other at the side of the jugular vein in the sinus 

 sternalis. They are sometimes quite close to the ventral 

 branchial body, and sometimes at some distance from it ; 

 they are greyish-red or yellowish in colour, and in adult speci- 

 mens of Bana esculento may reach 1 millimetre in diameter. 



The arteries to the corpuscles come from the musculo- 

 glandular branch of the external carotid. The veins pass 

 into the external jugular. 



There may be more than two glandules on either side. 



The parathyroid has a tough, fibrous capsule, and the 

 interior of the body is compact. There are closely placed 

 elliptical or spindle-shaped nuclei which stain deeply. The 

 cells are longish, and so disposed that they describe spiral 

 turns. The cell outlines of the glandules are distinct even 

 when viewed under a low power of the microscope. Some 

 of the nuclei are rounded, while others are distinctly elon- 

 gated. Some of the cells are vacuolated, probably owing 

 to the removal of fat droplets in the process of preparation 

 for microscopical examination. In some sections the disposi- 

 tion of the more central part of the organ is such as would be 

 found if the body had been subjected to a process of torsion. 

 The cells vary very considerably in shape ; they may be oval, 

 cubical, pentagonal, spheroidal, or elongated. 



(d) The post-branchial body is of considerable importance 

 in any discussion of the development of the thyroid body. 

 Its relationship to the latter body in higher vertebrates will 

 be fully discussed later (p. 261). De Meuron was the first 

 to discover the structure in the frog and in the toad, and 

 to work out its development. He considered that it is homo- 

 logous with the suprapericardial body which had been described 

 by v. Bemmelen in Elasmobranchs. Maurer has supported 

 this view, and introduced the name " post-branchial body " to 



