THE VASCULAR GLANDS. 



the temperature of the body in the reduced state to which they fall 

 during that time. 



THE THYROID. 



The Thyroid gland is situated in the neck. It consists of two lobes, 

 one on each side of the trachea extending upward to the thyroid cartilage, 

 covering its inferior cornu and part of its body; these lobes are connected 



FIG. 257. Part of a section of the human Thyroid, a, fibrous capsule; 6, thyroid vesicles filled 

 with, e, colloid substance; c, supporting fibrous tissue; d, short columnar cells lining vesicles; /, ar- 

 teries; gr, veins filled with blood; /i, lymphatic vessel filled with colloid substance. (S. K. Alcock.) 



across the middle line oy a middle lobe or isthmus. The thyroid is cov- 

 ered by the muscles of the neck. It is highly vascular, and varies in size 

 in different individuals. 



Structure. The gland is encased in a thin transparent layer of dense 

 areolar tissue, free from fot, containing elastic fibres. This capsule sends 

 in strong fibrous trabeculae, which enclose the thyroid vesicles which are 

 rounded or oblong irregular sacs, consisting of a wall of thin hyaline 

 membrane lined by a single layer of low cylindrical or cubical cells. 

 These vesicles are filled with a coagulable fluid or transparent colloid 

 material. The colloid substance increases with age, and the cavities 

 appear to coalesce. In the interstitial connective tissue is a round meshed 



