i66 THE HEAD AND NECK 



operation the trachea is opened below the isthmus of the thyreoid 

 gland, and the wound will necessarily be deep, as this part of 

 the trachea lies at some distance from the surface. On this 

 account the skin incision must be a long one, and it should 

 extend down to the jugular (supra-sternal) notch or on to the 

 sternum. It is vertical in direction, and passes through Burns's 

 space (p. in). In the cellular tissue which occupies the space, 

 the communicating branch between the two anterior jugular 

 veins must be found (Fig. 51), ligatured, and divided. The 

 posterior wall of the space is then cut through and a collection 

 of loose fat is encountered. In this fat, which also contains a 

 few lymph glands, the inferior thyreoid veins descend in front 

 of the trachea from the lower and medial surfaces of the lateral 

 lobes of the thyreoid gland. The veins of the two sides may 

 unite and join the left innominate vein, or they may open 

 separately into the right and left innominate veins. When 

 present, the thyreoidea ima artery ascends in this fat from the 

 innominate artery to the lower border of the isthmus of the 

 thyreoid gland. All these vessels may require to be tied before 

 the pretracheal fascia is divided. The trachea is then incised 

 from below r upwards lest any injury be done to the left innominate 

 vein or the innominate artery, which sometimes occupy a higher 

 position than usual. 



In children low tracheotomy may be rendered very difficult 

 owing to the shortness of the neck and the presence of the 

 thymus gland. Further, the position of the innominate artery 

 and the left innominate vein is slightly higher than in the adult. 

 The Thymus Gland is of considerable size in the fcetus ; 

 it undergoes little alteration in size during childhood, but there- 

 after it undergoes almost complete atrophy. It is enclosed in 

 a fascial sheath and lies in the superior mediastinum, in front 

 of the trachea and great vessels, and immediately behind the 

 manubrium sterni. Recent observations tend to show that in 

 the infant certain obscure conditions, which are associated with 

 dyspnoea and stridor, are due to hypertrophy of the thymus 

 gland, and the operation of subtotal subcapsular thymectomy has 

 been performed successfully in several cases. 



The method of approach is the same as that employed in 

 low tracheotomy. The gland is found behind the posterior 

 wall of Burns's space, and one lobe may be shelled out from its 

 sheath by blunt dissection. 



The Thyreoid Gland consists of an isthmus and two lateral 



