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C. M. JACKSON 



a. Norinal structure of the thyroid gtand 



The general form and topography of the thyroid gland in the 

 albino rat is shown in cross section in figure 1. Each lateral 

 lobe presents the typical relations — convex external surface cov- 

 ered by the infrahyoid musculature; conca^'e internal surface in 

 contact with the lower larynx and upper trachea; and narrower 

 posterior surface (or border) in relation with the oesophagus 



Fig. 1 From a photograph (retouched^ of a cross set-tiou of the thj-roid gland 

 in situ at the level of the isthmus, showing relations to infrahyoid musculature, 

 uppermost trachea, oesophagus, etc. One parathyroid is visible, on the left side 

 of the figure. From albino rat No. S 9.47, age 22 days, gross body-weight 

 25.5 grams. (X 28.) 



medially the carotid artery, etc., laterally. The isthmus is fre- 

 quently a very thin somewhat fibrous band, almost invisible 

 when the fresh gland is exposed in situ. It invariably contains 

 thyroid follicles (contrary to Sobotta '15), although these may 

 become scattered and more or less atrophied in adult rats. 



The minute structure of the normal thyroid gland at 3 weeks 

 (the age when the experiments began with the younger rats) is 

 shown with slight magnification in figure 1 , and under high power 

 in figure 2. No attempt will l)e made to describe in detail the 



