THYROID GLAND. 421 



bution is unknown. In the medullary substance, however, there are two 

 ganglia situated close to the central vein. 



Nothing is known of lymphatics in the suprarenal capsules, and the exist- 

 ence of such vessels is doubtful. 



Chemical Reactions of the Suprarenal Capsules. Vulpian has described 

 (1856), in the medullary portion of the suprarenal capsules, a peculiar sub- 

 stance, soluble in water and in alcohol, which gave a greenish reaction with 

 the salts of iron and a peculiar rose-tint on the addition of iodine. He 

 could not determine the same reaction with extracts from any other parts. 

 Later, in conjunction with Cloez, he discovered hippuric and taurocholic 

 acid in the capsules of some of the herbivora. These bodies contain in 

 addition, leucine, hypoxanthine, taurine, fats and inorganic salts, the latter 

 chiefly phosphates and salts of potassium. 



The suprarenal capsules are not essential to life. If care be taken to 

 avoid injury of the semilunar ganglia, they may be removed from animals 

 and the operation apparently has no remote effects. In Addison's disease, a 

 disorder attended with bronzing of the skin and serious and finally fatal dis- 

 order of nutrition, there usually is disorganization of the suprarenal capsules, 

 but this is not invariable. It is not established that disorganization of the 

 capsules stands in a causative relation to the discoloration of the skin or to 

 the constitutional disturbance. Investigations into these diseased conditions 

 have developed little -or nothing of importance concerning the physiology of 

 the suprarenal capsules. 



THYROID GLAKD. 



The thyroid gland is attached to the lower part of the larynx and follows 

 it in its movements. Its color is brownish-red. The anterior face is convex 

 and is covered by certain of the muscles of the neck. The posterior surface 

 is concave and is applied to the larynx and trachea. It presents two lateral 

 lobes, each with a rounded, thickened base below, and a long, pointed extrem- 

 ity extending upward, the lobes being connected by an isthmus (see Fig. 141, 

 page 424). Each of these lobes is about two inches (50 mm.) in length, 

 three-quarters of an inch (19 mm.) in breadth, and about the same in thick- 

 ness at its thickest portion. The isthmus connects the lower portion of the 

 lateral lobes, covers the second and third tracheal rings, and is about half an 

 inch (12 mm.) wide and one-third of an inch (8'5 mm.) thick. From the 

 left side of the isthmus, and sometimes from the left lobe, is a portion pro- 

 jecting upward, called the pyramid. The weight of the thyroid gland, 

 according to Sappey, is three hundred and fifty to three hundred and eighty 

 grains (22 to 24 grammes). It is usually stated by anatomical writers that 

 it is relatively larger in the foetus and in early life than in the adult ; but 

 according to Sappey, its weight, in proportion to the weight of the adjacent 

 organs, does not vary with age. It is a little larger and more prominent in 

 the female than in the male. 



Structure of the Thyroid Gland. The thyroid gland is covered with a 

 thin but resisting coat of ordinary fibrous tissue, which is loosely connected 



