chap, ix.] THE LARYNX AND TRACPIEA. 137 



the cannula, if the tracheal wound be missed, it is 

 easy to thrust the instrument into the lax tissue be- 

 neath the cervical fascia and imagine that it is within 

 the windpipe. 



In laryngotomy the air passage is opened by a trans- 

 verse cut through the crico-thyroid membrane. The 

 crico- thyroid space only measures about half an inch 

 in vertical height in well-developed adult subjects, 

 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 

 even fatal haemorrhage has occurred from these vessels " 

 (Durham). In introducing the cannula it may readily 

 slip between the crico-thyroid membrane and the 

 mucous lining instead of entering the trachea. 



Foreign bodies often find their way into the 

 air passages, and have been represented by articles of 

 food, teeth, pills, buttons, small stones, and the like. 

 They are usually inspired during the act of respiration, 

 and may lodge in the superior aperture of the larynx, 

 or in the rima, or find their way into the ventricle, 

 or lodge in the trachea, or enter a bronchus. If a 

 foreign substance enters a bronchus it usually selects 

 the right, that bronchus having its aperture more im- 

 mediately under the centre of the trachea than has 

 the left tube. Quite recently, in a dissecting-room 

 subject, I found two threepenny pieces lying side by 

 side, in the right bronchus, so as to entirely block the 

 tube. The danger of inhaled foreign substances de- 

 pends not so much upon the mechanical obstruction 

 they offer, as upon the spasm of the glottis they excite 

 by reflex irritation. A body may, however, lodge in the 

 ventricle for some time without causing much trouble, 

 as in a case reported by Desault, where a cherry-stone 



