1 6 LANDMARKS MEDICAL AND SURGICAL. 



the neck in an easy position, the distance is barely one inch 

 and a half. When the neck is well stretched, about three- 

 quarters of an inch more is gained. Thus, we have 

 (generally) not more than seven or eight rings of the 

 trachea above the sternum. None of these rings can be 

 felt externally. The second, third, and fourth are covered 

 by the isthmus of the thyroid gland. The trachea, it should 

 be remembered, recedes from the surface more and more 

 as it descends, so that, just above the sternum in a short 

 fat-necked adult, the front of the trachea would be quite 

 one inch and a half from the skin. 



27. Trachea. In the dead subject nothing is more easy 

 than to open the trachea : in the living, this operation may be 

 attended with the greatest difficulties. In urgent dyspnoea you 

 must expect to find the patient with his head bent forward, 

 and the chin dropped, so as to relax as much as possible the 

 parts. On raising his head, a paroxysm of dyspnoea is almost 

 sure to come on, threatening instant suffocation. The elevator 

 and depressor muscles draw the trachea and larynx up and 

 down with a rapidity and a force which may bring the cricoid 

 cartilage within half an inch of the sternum. The great 

 thyroid veins which descend in front of the trachea are sure 

 to be distended. There may be a middle thyroid artery. 

 In children the lobes of the thymus may extend up in front 

 of the trachea, and the left vena innominata may cross it 

 unusually high. Thus the air-tube may be covered by 

 important parts which ought not to be cut. Considering all 

 these possible complications, the least difficult and the best 

 mode of proceeding is to open the trachea just below the 

 cricoid cartilage ; and if more room be requisite, to pull 

 down the isthmus of the thyroid gland, or in children 

 to divide the cricoid itself. It is important that all the 

 incisions be made strictly in the middle line, the ' line of 

 safety.' 



28. Sterno-mastoid muscle. The sterno-mastoid muscle 

 is the great surgical landmark of the neck. It stands out in 

 bold relief when the head turns towards the opposite shoulder. 

 Its inner border overlaps the common carotid, which can be 



