80 SURGICAL ANATOMY OF THE 



Laryngotomy, in which the crico-thyroid membrane 

 is divided ; this is the readiest method of admitting air, 

 the only difficulty which might arise being the hemor- 

 rhage from the crico-thyroid arteries, which run across 

 this space. The incision in the membrane, which is 

 made horizontally, must not be "so wide as to injure the 

 crico-thyroid muscles. 



Tracheotomy is the operation in which the rings of the 

 trachea are divided either above or below the isthmus of 

 the thyroid body. It must be borne in mind that, 

 although the trachea is very superficial above, it recedes, 

 and is very deep below, and, just above the sternum is 

 generally at least an inch from the surface, its depth 

 varying according to the amount of fat or muscle in the 

 individual, or to the incurvation of the cervical vertebrae. 

 It is crossed at about its second or third rings by the 

 isthmus of the thyroid body, and below the isthmus, on 

 the lower part of the trachea, lie the middle and inferior 

 thyroid veins, which are generally greatly engorged, on 

 account of the asphyxia necessitating the operation. 

 Occasionally the rings are ossified in old persons, and 

 may cause trouble. 



In children, owing to the shortness of the neck, and 

 the depth, small calibre, and mobility of the trachea, 

 the operation is a difficult one. Again, the plexus of 

 veins in connection with the thyroid body and the close- 

 ness of the carotids, render it one demanding the greatest 

 care. The innominate is proportionably higher up in 

 the neck than in the adult, on account of its obliquity. 

 In children under two years of age, and in some in- 

 stances far older, the thymus gland may give great 

 trouble by bulging up into the wound, and so obstruct- 

 ing the operator's view of the parts. 



