THYMUS GLAND 



919 



It is common]}' made up of two elongated, nearly equal pyramidal lo})es of a 

 greyish pink colour, which meet each other near the middle "line; Imt they vary 

 in number and are inconstant in size. There may be but a single lobe present or 

 a third may intervene between the other two.' Sometimes the right lol)e and 

 sometimes the left lol)e is the larger. 



The thymus body is about two inches (50 mm.) in length, about one inch and 

 a half (87 mm.) in breadth at its base, and a quarter of an inch (16 mm.) in 

 thickness. 



Its weight at l)irth is about half an ounce. 



Relations.— The thymus body at the period of its fullest development lies 



Fk;. r)41.— TnvMts Gi.axd tx a Child at the Age ok Two Yeaes. 



SEVENTH Ring of trachea 

 Ritjht carotid arterij 



Kiff/it fiibclaiian artery 



IHnlii i'momiiiale rein 



THYMUS GLAND 

 Vena rara superior 



A rch of aorta 



THYROID CARTILAGE 



Central portion of crico-thyroid 



membrane 

 Crieo-thyroid muscle 



FIRST RING OF TRACHEA 



THYROID BODY 



Ligament connecting thyroid 

 and thymus bodies 



Left carotid artery 



Li ft xubclavian intery 



LOBE OF THYMUS PASSING 

 BEHIND VEIN 



innominate rein 



A icli of aorta 



w 



jtartlv in the thorax and partly in the neck. It extends upwards as far as the 

 thyroid body covered Ity the stcrno-hyoid and thyroid muscles, completely hiding 

 the trachea and the carotid sheaths. Below, it descends into the superior niedias- 

 tinum between the pleural sacs and internal mammary vessels as far as the fourth 

 rib cartilages, and lies l)ehind the sternum, the sterno-hyoid, and stemo-thyroid 

 muscles, and in front of the pericardium and larger vessels. 



Structure. — A thin areolar capsule invests the lobes of the thymus gland, and 

 extends ujjwards in the form of two flattened fibrous bands to be attached to each 

 lobe of the thyroid body. These bands are well marked at the period of liirth, and 

 seem to act as susi)ensory ligaments. If the capsule is removed, it is .><een to send 



