260 THE DUCTLESS GLANDS 



express its relation to the gill-clefts. V. Bemmelen looked 

 upon his suprapericardial bodies as homologous with gill- 

 clefts, but Maurer considers them to be of a different nature, 

 because in all vertebrate animals in which they occur they 

 arise immediately behind the last gill-cleft, whether this be 

 the fourth, fifth, or sixth. 



The post-branchial body has so far been discovered in all 

 Gnathostomata, but in many forms it appears only on one side. 



The post-branchial body of the frog is a tiny structure which 

 lies at the side of the aditus laryngis under the epithelium of 

 the floor of the pharynx. It consists of three or four small 

 vesicles lined with cylindrical epithelium. Maurer states that 

 these cells sometimes carry cilia. The vesicles contain a 

 coagulated albuminous substance and debris, but no colloid. 



6. In Reptilia the thyroid is unpaired in some families 

 (Ophidia and Chelonia), while in the Lacertilia the organ is 

 bilobed in young specimens, paired in older ones. The organ 

 lies immediately in front of the pericardium. The parathy- 

 roids and post-branchial bodies are intimately united, paired, 

 and placed anteriorly to the thyroid. Their precise anatomy 

 differs in different groups. The thyroid gland presents no 

 special features so far as microscopical structure is concerned. 



In Chrysemys picta and Pseudemys scripta the parathyroid 

 contains vesicles, and in the latter species some of these 

 vesicles contain colloid. 



In C. picta the post-branchial body also contains colloid, 

 but the parathyroid and post-branchial body are very con- 

 siderably confused together in this and some other species. 



In Testudo grceca there exists on each side an " inferior 

 internal" parathyroid, applied to the carotid ("glandule 

 parathyroidienne "), and a "superior external" parathyroid 

 included within the substance of the thymus ("glandule 

 parathymique "). These bodies are about 1 millimetre in 

 size, round, oval, or triangular, and possess processes which 

 may be as long as the organ itself. The glandule which is 

 embedded in the thymus is particularly rich in such processes 

 (Aime). 



7. In Aves the general features of the thyroid are the 

 same as in reptiles. The adult gland is a paired organ placed 

 near to the large vessels of the neck. The vesicles are fre- 

 quently small and irregular in outline. The intervesicular 



