THYMUS GLAND 467 



The superior and inferior thyroid arteries, sometimes a 

 thyroidea ima branch from the innominate artery, supply the 

 gland. The veins are the superior and inferior accessory 

 thyroids, a transverse, and sometimes a middle thyroid vein. 

 The lymphatics drain into the superior and inferior set of deep 

 cervical nodes, and the nodes in front of the bifurcation of the 

 trachea; also an ascending trunk passes to the node in front 

 of the larynx. The nerves are derived from the inferior laryngeal 

 and the middle and inferior cervical ganglion of the sympathetic. 

 The accessory thyroids are small isolated masses of thyroid 

 tissue sometimes present, found about the lateral lobes of the 

 thyroid gland in the sides of the neck or just above the hyoid 

 bone. 



PARATHYROID GLANDS 



The parathyroid glands are small reddish-brown bodies, 

 composed of masses of cells, arranged in a more or less reticular 

 manner, with numerous intervening bloodvessels. They are 

 usually found one on either side (the superior) at the level of 

 the lower border of the cricoid cartilage, behind the junction 

 of the pharynx and esophagus, and in front of the prevertebral 

 fascia. The lower are just below the lower edge of the lateral 

 lobe one on either side. There are usually four, but may be 

 only three, or, again, as many as six or eight. Their location 

 is variable. 



THYMUS GLAND 



The thymus gland is a temporary organ, attaining its full 

 size at the end of the second year and gradually shrinking 

 until puberty, when it entirely disappears. Consists of two 

 lateral lobes placed in close contact along the median line. It 

 is found in the superior mediastinum, covered by the sternum 

 and the origins of the sternohyoid and sternothyroid muscles; 

 below, it rests upon the pericardium, and separated from the 

 arch of the aorta and great vessels by fascia. In the neck it 

 lies on the front and sides of the trachea beneath the sterno- 

 hyoid and sternothyroid muscles. It is pinkish gray in color. 

 About 2 inches in length, 1-J- inches in breadth, below, and 

 about J inch in thickness. 



