26 INTERNAL SECRETION 



The sexual glands and other tissues concerned in the processes 

 of reproduction ; 



The pancreas ; 



The intestinal and gastric mucosa ; 



The kidneys. 



It is not proposed to enter into the questions of glycogenesis 

 and the neutralizing activity of the liver. These secretory func- 

 tions are the oldest known to us and are fully described in the 

 current text-books of physiology. 



The plan adopted in each instance is : First, to give the 

 necessary information concerning the morphology and the 

 development of the organ ; second, to describe in detail its 

 physiological and experimental aspects; and finally, to estimate 

 its pathological significance by means of material gained from 

 clinical observation. 



THE THYROID APPARATUS. 



The thyroid apparatus comprises two distinct organic systems 

 which differ both in structure and in function. They are the 

 thyroid gland, Glandula thyroidea, and the parathyroid glands, 

 Glandules parathyroidece. 



ANATOMY. 



The thyroid gland of man consists of two lateral lobes, 

 situated upon the lateral surface of the larynx, united by a 

 transverse portion, the isthmus. Accessory lobes (Glandules 

 thyroidecc aberrantes), distinct from the principal organ, may 

 occur within a triangular area, the apex of which is at the root of 

 the aorta, the base being formed by the edge of the lower jaw. 

 In animals these accessory glands may prejudice the results of 

 experiment, while in man they may give rise to retrosternal 

 goitres and so acquire a pathological significance. 



The thyroid gland is remarkably vascular, being supplied 

 with blood by no less than three to five large arteries. According to 

 Tschuewsky, the whole of the blood in the body of the dog passes 

 through the thyroicl sixteen times a day. 



The blood is carried away from the gland by a system of 

 large veins. The lymph passages, which are present in large 

 numbers, open into the deep cervical glands. The nerves, which 

 are comparatively scanty, proceed in part from the ganglia of 

 the cervical sympathetic nerve and in part from the superior 

 laryngeal nerve. 



HISTOLOGY. 



In an early stage of development the thyroid gland is a 

 compound tubular gland with a duct (ductus thyroglossus), which 



