THE THYMUS GLAND. 613 



THE THYMUS GLAND. 



This body is noticed here from being located in the vicin- 

 ity of the thoracic organs, rather than from any thing that 

 is especially known of its physiological relationships. 



It is situated in the anterior mediastinum, occupying a 

 greater part of its extent. During foetal life, and for the 

 first year or two after birth, it descends in front of the 

 pericardium nearly as low as the diaphragm, and ascends 

 upon the neck as high as the thyroid gland. After the 

 second year it commences diminishing till, at the period of 

 puberty, scarcely a vestige of it remains. Cases, however, 

 are not wanting in which it has been seen at from 20 to 

 30 years, even larger than in children, and even from 30 

 to 50 it has been found of considerable size. This body, 

 though called a gland, is destitute of one of the great char- 

 acteristics of a gland proper, an excretory duct. It is a sym- 

 metrical body, consisting of two lobes, of an oblong form, 

 which are connected as well as separated by cellular tissue. 



Structure. The lobes of the thymus are divisible into 

 lobules, which, according to the observations of Sir Astley 

 Cooper, consist of vesicles of different sizes connected by cel- 

 lular tissue, which also forms a common capsule to the gland 

 itself. These vesicles or cells communicate with a central 

 cavity or reservoir, which contains a milky fluid, like chyle. 

 This cavity is lined by a vascular mucous membrane, on the 

 surface of which the opening cells are seen. The consist- 

 ence of this gland is soft, and its color of a pinkish hue. 



Its arteries come from the superior and inferior* thyroid, 

 and internal mammary. Its veins go to the thyroid, and 

 vena innominata. The lymphatics join the absorbents at 

 their junction with the internal jugular and subclavian 

 veins. The nerves are derived from the internal mammary 

 plexus of the sympathetic. 



Function. The use of this body is yet unknown, though 

 its great importance to foetal life is admitted by all. Sir 

 A. Cooper suggests that the milk-like fluid found in its 

 cavity is furnished by it for the purpose of nourishing the 



