CHAPTER II 



THE DISEASES OF THE THYROID GLAND 



Anatomy and Embryology. The thyroid gland of man has the shape of a 

 butterfly. The two lobes lying on the lateral surfaces of the trachea and 

 larynx are joined together by the isthmus, which is sometimes prolonged 

 for a certain distance superiorly as the so-called processus pyramidalis. 

 The weight of the thyroid gland in the adult approximates 36-50 gm. 



The isthmus is developed from an unpaired evagination from the ventral 

 wall of the head-gut cavity. In many of the lower animal classes the con- 

 nection with the head-gut the ductus thyroglossus is retained. Here the 

 thyroid is a gland with external secretion. In the higher animal classes the 

 ductus thyroglossus obliterates early. Con- 

 cerning the development of the lateral lobes 

 opinions to-day are still divided. It is safe 

 to say that a portion of the lateral thyroid 

 gland rests are developed through evagina- 

 tion from the median rest. It is further 

 certain, according to the investigations of 

 Erdheim and Schilder, that the so-called post- 

 branchial bodies, that originate from the 

 ventral wall of the fourth branchial pouch, 

 can give rise to thyroid gland tissue, for in F>- 3 . Tr = Thyroid; /, //, 

 the cases of thyroaplasia in which the me- 7// ' IV = P har y^ eal P uche *; '** 



. = rudiments of the parathyroid 



dmm rests of the thyroid remain rudimentary, glands; p = Abranchial bodies; 



the indifferent rests of these bodies regularly Tm = rudiment of thymus. 

 contain some thyroid gland follicles. Only 



uncertain, therefore, is to what extent -under normal conditions the lateral 

 rests of the thyroid gland take part in the formation of the lateral lobes. 

 To aid the better comprehension of the subject, I subjoin the accompany- 

 ing sketch taken from the work of Maurer in which is shown the devel- 

 opment of the parathyroid and the thymus glands. 



The rudiments of the thyroid wander downward with the heart. Along the entire 

 tract from the root of the tongue to the aorta may be found cut-off portions of thyroid 

 glandular tissue, accessory thyroids, which may give occasion to the formation of ab- 

 normally situated goiters (tongue goiters, retrosternal goiters, etc.). 



The thyroid is remarkably well vascularized. It consists histologically 

 of follicles lined with cubical or cylindrical epithelium, which for the most 



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