THE NECK 163 



nerve and the inferior laryngeal artery pass upwards under cover 

 of the muscle, and may be divided at this stage. The trachea 

 is cut through near the cricoid cartilage, and its lower end is 

 turned forwards and stitched to the lower margin of the skin 

 incision, since it tends to retract into the thorax. 



The larynx is next retracted upwards and forwards, and the 

 inferior constrictor and the stylo -pharyngeus are divided. In 

 separating the larynx from the lower part of the pharynx, 

 care must be taken not to " button-hole " the mucous membrane 

 on the posterior aspect of the cricoid (p. 189). At the upper 

 border of the cricoid the pharynx is opened, and the epiglottis 

 may be cut across if it is not involved. The larynx is now only 

 fixed above and in front. The thyreo-hyoid muscle and mem- 

 brane are divided, and the cut is carried backwards through the 

 subjacent pad of fat till the divided epiglottis is reached. After 

 division of the internal laryngeal nerve and its accompanying 

 artery the larynx can be removed. If the epiglottis is involved 

 in the disease, the latter part of the operation follows the course 

 of a sub-hyoid pharyngotomy. 



The Trachea begins immediately below the cricoid car- 

 tilage, and ends opposite the lower border of the fourth thoracic 

 vertebra by dividing into the two bronchi. It is about 4^ inches 

 long, and its diameter varies from f inch to one inch. The 

 cervical part of the trachea is 2| inches long, and as it descends 

 it becomes more deeply placed, so that at the upper border of the 

 manubrium sterni it lies i| inches from the surface. In children 

 of from three to five years of age the cervical part of the 

 trachea is ij inches long and only inch wide. These 

 measurements give some indication of the variations necessary 

 in the diameters of tracheotomy tubes. 



The trachea is freely movable, since it is surrounded by loose 

 cellular tissue, and when necessary it can be retracted to one or 

 other side without much difficulty. The isthmus of the thyreoid 

 gland lies in front of the second, third, and fourth rings of the 

 trachea, while the lateral lobes lie one on each side in relation 

 to the upper six rings and to the cricoid and thyreoid cartilages. 



The posterior surface of the trachea, which is in contact 

 with the oesophagus, is flattened so that the tube is horseshoe- 

 shaped on section. This is due to a deficiency in the cartilagin- 

 ous rings posteriorly. The posterior wall consists of the mucous 

 membrane and the fibro-elastic coat of the trachea. If the 

 surgeon, in performing tracheotomy, opens the trachea too 



