136 SURGICAL APPLIED ANATOMY. [Chap. ix. 



branch between the superior thyroid veins is sometimes 

 found. Over the isthmus is a venous plexus, from 

 which the inferior thyroid veins arise, while below the 

 isthmus these veins lie in front of the trachea together 

 with the thyroidea ima artery (when it exists). The 

 inferior thyroid vein may be represented by a single 

 trunk occupying the middle line. In the infant before 

 the age of two years the thymus extends up for 

 a variable distance in front of the trachea. At 

 the very root of the neck the trachea is crossed by the 

 innominate and left carotid arteries and by the left in- 

 nominate vein ; and lastly, abnormal branches of the 

 superior thyroid artery may cross the upper rings 

 of the windpipe.* 



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.,loj 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 introducing 



* See an excellent article on the anatomy of this region by Dr. 

 Pilcher, "Annals of Anatomy and Surgery." New York, April, 

 1881. 



