476 Ealph H. Major. 



mal. I wish here also to express my thanks to Dr. H. M. Evans for 

 the use of several injected specimens of human thyroids which he 

 had injected in connection with his work upon the parathyroids (3). 

 The histological structure of the thyroid has been the subject of 

 considerable literature in the past. Baber's (4) classical studies of 

 the minute anatomy. of the structure of the thyroid gland was one of 

 the most important of the early contributions to this subject. He 

 described particularly the histology of the follicles and the lymphatics. 

 Langendorff (6), Wolfler (7), Lustig (8), Biondi (9), Hiirtle 

 (10), Andersson (11), Kohn (12), Streif (13), Flint 

 (14), Coco (15), and others have given us important contri- 

 butions upon the subject. These studies show that consid- 

 erable differences of opinion have existed as regards its histological 

 structure. Wolfler found that the thyroid of the child as well as 

 of the adult contains solid rows of cells at the periphery while the 

 center of the gland is composed mostly of vesicles filled with colloid 

 material. He does not seem, however, to have attempted to divide 

 it definitely into a cortical and medullary portion. Flint does not 

 believe that thyroid gland, of the dog and man at least, can be di- 

 vided into either lobes or lobules, but that the septa from the capsule 

 penetrate the parenchyma of the gland in an irregular fashion. He 

 has, however, observed pictures that suggest definite lobulation, but 

 thinks that if the original lobulation is present in the embryo it is 

 later lost. Eegaut and Petti jean (16) studying the dog, cat, pig and 

 other animals also do not believe that the thyroid gland can be divided 

 into lobules. They maintain that there is no such architecture present, 

 that there is no distribution of blood vessels or lymphatics to war- 

 rant the conception of a lobule. Coco (15) gives a description of the 

 structure of the dog's thyroid that summarizes and agrees in general 

 with the conclusions of most observers, and with the descriptions 

 in most text-books. According to him, the thyroid gland is surrounded 

 completely by a thick capsule which gives off numerous prolonga- 

 tions of connective tissue. These septa penetrate the parenchyma 

 of the gland, dividing and sub-dividing it into lobes and lobules. 

 The septa which also support blood-vessels and nerves, become thin- 

 ner and thinner and finally end by surrounding each follicle in the 



