SECRETION. 401 



* 



sides of the upper extremity of the trachea. It consists of a pair 

 of lateral lobes united at their lower part by a transverse isthmus. 

 The lateral lobes are oblong, oval, thicker below than above, and 

 usually of unequal length. The weight of the thyroid is usually 

 from one to two ounces, but is larger in the female. It is very liable 

 to become hypertrophied, especially in the female; then it is called 

 goiter. 



The thyroid is a highly vascular organ, invested with a thin, 

 fibrous membrane, and composed of a fibrous stroma, in the meshes 

 of which a multitude of minute closed vesicles exist. 



-5 



4 



Fig. 144. Structure of the Thyroid (Morat and Doyon). Lobule of 

 the Thyroid after an Injection of the Lymphatic Vessels with Nitrate 

 of Silver. Semi-schematic. (VIALLETON. ) 



1, 1, Vesicles. 2, Their colloid contents. 3, 3, Lymphatic vessels with epithe- 

 lium stained with silver. 4, Blood capillary. 5, 5, Cells in the walls of the 

 vesicles. 



Each little lobule seems to be a completely closed sac at least, 

 no tubule is noticed emanating from it. The little sacs are filled 

 with a transparent, amber-colored, viscid, nucleo-albuminous fluid. 

 In the connective tissue surrounding each lobule there is a plexus 

 of capillaries. With them there is found an abundant supply of 

 lymphatics. 



Vessels and Nerves. The arterial supply for the thyroid body 

 is gained from the superior and inferior thyroid arteries. These 

 arteries are remarkable for their large size and numerous anasto- 

 moses. The veins^form a plexus upon the front of the trachea and 

 surface of the gland. From the plexus arise the superior, middle, 



