chap, ix.j THE NECK. 157 



The evil of wounding the thyroid isthmus is 

 greatly exaggerated. I have frequently divided this 

 structure in performing tracheotomy without any in- 

 convenience resulting. Like other median raphe, the 

 middle line of the thyroid isthmus has but a slight 

 vascularity, and it has been shown that one side of 

 the thyroid gland cannot be injected from the other 

 (i.e. by injection that would cross the isthmus). The 

 difficulty of tracheotomy in infants depends upon the 

 shortness of the neck, the amount of the subcutaneous 

 fat, the depth at which the trachea lies, its small size, 

 its great mobility, and the ease with which it can be 

 made to collapse on pressure. To the finger, roughly 

 introduced, the infant's trachea offers little resistance. 

 Its mobility is such that we hear of its being held aside 

 unknowingly by retractors, while the operator is 

 scoring the oesophagus (Durham). In the child also 

 the great vessels often cross the trachea higher up than 

 in the adult, and some inconvenience may also arise 

 from an unduly prominent thymus. In one case, in 

 an infant, the end of a tracheotomy tube pressing on 

 the front of the trachea produced an ulcer that opened 

 the innominate artery (Brit. Med. Jour., 1885). In 

 introducing the cannula, if the tracheal wound be 

 missed, it is easy to thrust the instrument into the 

 lax tissue beneath the cervical fascia and imagine 

 that it is within the windpipe. 



In laryngotomy the air passage is opened by a 

 transverse cut through the crico-thyroid membrane. 

 The crico-thyroid space only measures about half an 

 inch in vertical height in well-developed adult sub- 

 jects, while in children it is much too small to allow of 

 a cannula being introduced. The crico-thyroid arteries 

 cross the space, and can hardly escape division. They 

 are, as a rule, of very insignificant size, and give no 

 trouble. Occasionally, however, these vessels are 

 large, and " cases are recorded in which serious and 



