STRUCTURE OF THE THYROID BODY. 



191 



animals contain a brownish pigment, but in man the dark red colour of 

 the medulla is largely due to the blood contained in the large venous 

 spaces by which it is pervaded, and which receive the blood after it has 

 traversed the capillaries of the cortex. Investing the larger veins are 

 longitudinal bundles of plain muscular fibres ; and numerous nerves, 

 after traversing the cortical substance, are distributed throughout the 

 medulla, where they form a close plexus provided with ganglion-cells. 

 The cells of the medulla are characterised by staining brown by chromic 

 acid and its salts, provided the organ is quite fresh. 



THE THYROID BODY. 



The thyroid body consists of a framework of connective tissue in- 

 closing numerous spherical or oval vesicles (fig. 225) which are lined 

 with cubical epithelium. The cavities of the vesicles are filled with a 

 peculiar viscid liquid which is coagulated by alcohol and which then 

 becomes stained with hrernatoxylin. A similar material has been found 



FIG. 225. SECTION OF THE THYROID GLAND OF A CHILD. 



Two complete vesicles and portions of others are represented. The vesicles are filled with 

 colloid, which also occupies the interstitial spaces. In the middle of one of the spaces a 

 blood-vessel is seen cut obliquely, and close to it is a plasma-cell. Between the cubical 

 epithelium-cells smaller cells like lymph-corpuscles are here and there seen. 



in the lymphatics of the gland, and may sometimes be detected also in 

 the interstices of the connective tissue, as shown in the figure. 



The blood-vessels of the thyroid are exceedingly numerous, and the 

 capillaries form close plexuses round the vesicles. Some of the blood- 

 vessels are distributed to a peculiar highly vascular embryonic tissue 

 which occurs in patches here and there in the organ (Horsley). 



Disease of the thyroid or its extirpation is accompanied by remark- 

 able changes in the chemical composition of the blood and many of the 

 tissues, resulting chiefly in the accumulation within them of a large 

 amount of mucin ; a condition of general myxcedema, and eventually of 

 cretinism, being produced. 



