160 VISCERAL ANATOMY. 



Enumerate the Veins and Nerves of the Thyroid Gland. The 

 Veins form a plexus in front of the gland and the trachea, giving rise to the 



Superior Thyroid Vein. ") 



,/., -~ . . r , . > open into the Internal Jugular Vein. 



Middle Thyroid Vein. ) J 



Inferior Thyroid Vein, opens into the Innominate Vein. 

 Nerves are branches of the pneumogastric, and of the middle and 

 inferior ganglia of the sympathetic. 



THE THYMUS GLAND. 



What is the Thymus Gland ? It is a temporary organ, attaining its 

 full size about the age of 2 years, then being about 2 inches long, ij^ inch 

 broad, 3 lines thick, and weighing about half an ounce. It subsequently 

 atrophies, and has almost disappeared at puberty. It is situated in the anterior 

 mediastinum and the neck, behind the sternum and the sterno-hyoid and 

 sterno-thyroid muscles, extending from the level of the 4th costal cartilage to 

 the lower border of the thyroid gland. In the mediastinum it rests upon the 

 pericardium, and is separated by the thoracic fascia from the arch of the aorta 

 and the great vessels. 



Describe its Structure. The Thymus gland consists of two lateral lobes 

 (sometimes a third), together forming a pyramidal mass. It is surrounded by 

 a (ibrous capsule and is divided by Trabeculce into primary and secondary 

 lobules, which consist of meshes of delicate retiform tissue closely packed 

 with lymph-corpuscles, and pervaded with capillaries. The so-called Central 

 Cavity and Primitive Linear Tube, are deceptive appearances of the multi- 

 plying cells in the interior of the gland. 



Name its Vessels and Nerves. The Thymus 

 Arteries, are derived from the internal mammary, superior and inferior 



thyroid, subclavian and carotid. They ramify on the surface of each lobule, 



having smaller twigs converging toward the centre. 

 Veins, open into the left innominate and the thyroid. 

 Lymphatics, consist of intralobular and interlobular plexuses, and open into 



the anterior mediastinal glands. 

 Nerves, are very minute and derived from the pneumogastric and the sym 



pathetic. 



THE SUPRA-RENAL CAPSULES. 



What are the Supra-Renal Capsules ? They are two small, crescentic- 

 shaped bodies, situated one on each kidney. Each presents a small fissure or 

 Hilum anteriorly, from which its vein emerges, and consists of a 



Fibrous Capsule, which is very thin, closely adherent, and sends numerous 

 septa inwards. 



