THE THYKOID BODY. 



415 



THE THYROID BODY. 



The thyroid body is a dark red, vascular organ, composed 

 of two lobes. It seems very possible that we may now legiti- 

 mately call it a secreting gland, whose product acts upon the 

 red blood-cells, and is carried away by the lymphatics. 



The entire organ is enclosed in a thin, but firm, fibrous cap- 

 sule. This sends off processes to the interior, which interlace, 

 forming a sponge-like network. This network is thin, however, 

 and does not make up much of the substance of the gland. A 

 few elastic fibres run in it. Enclosed in the meshes of the frame- 

 work thus formed are the vesicles of the gland. These are 

 very numerous and make up the bulk of the organ. They are 

 minute, spherical, ovoid, or flattened bodies, whose diameter 

 is from yfg- mm. in the embryo to 2 mm. in the adult, and are 

 grouped into small lobules of various sizes. They consist of 

 a homogeneous connective-tissue basement-membrane, lining 

 which is a single layer of epithelial cells, the whole enclosing 

 a yellowish, transparent, viscid fluid. The 

 lining-cells, in adults, measure about yf-g- 

 mm. in height and y^ mm. in width. They 

 contain nuclei, and sometimes nucleoli. 

 They are loosely connected to the base- 

 ment-membrane, and, with extra-uterine 

 life, begin to break away into the interior 

 of the vesicle. Baber describes fine, longi- 

 tudinal striae passing from the base toward 

 the apex of the cell. These cells have a 

 tendency to undergo colloid degeneration. 

 The cell-body swells up, and bursting, the 

 contents spread out in the vesicle-cavity, 

 there to undergo or complete the metamor- 

 phosis (Fig. 178) mentioned. According 

 to Baber, however, the cells which undergo this degenera- 

 tion come from the connective tissue surrounding the vesicles. 

 They pass through the vesicle-wall into its cavity, and there 

 'gradually break up. This change goes on at the expense of 

 *the vesicle-wall and the intervesicular tissue, so that in time 

 the gland, without being much enlarged, may appear, on sec- 

 tion, almost like a single colloid mass. 



Pio. 178. Colloid metamor- 

 phosis : a, Gland vesicle of the 

 rabbit ; 6, commencing colloid 

 metamorphosis of the calf. 

 Frey. 



