700 OPEEATIOJNS. 



between the skin and the shield, when the swelling caused by the 

 operation subsides. Field's tube is a very good one for temporary 

 use. 



SITE OF OPENING. — For permanent tracheotomy, there are 

 three conditions which regulate the position of the opening in the 

 windpipe. (1) It should be on a spot where the muscles covering 

 the windpipe are not thick. (2) It should be sufficiently high, so 

 as to allow of a second opening being made, in the event of 

 changes (narrowing of the windpipe from distortion, ossification, 

 etc.) occurring in the neighbourhood of the first opening which 

 would interfere with the breathing. (3) It should be sufficiently 

 low down to prevent the horse disturbing the tube in any way 

 by drawing in his head (flexing his head on his neck). These 

 conditions will generally be fulfilled if the opening be made at a 

 distance of about 5 inches (Fig. 183) from the larynx. Mr. Jones 

 advised that the operator should always see the horse ridden with 

 the bridle he regularly wears, so as to observe the position in which 

 the animal carries his head, and to find out if he is accustomed 

 to arch his neck a good deal; for in that case the tube must be 

 inserted lower down than otherwise. 



In temporary tracheotomy, it is best to make the opening about 

 half-way down the neck (that is, about half-way between the larynx 

 and the breast) ;. at that spot, the windpipe occupies a more super- 

 ficial position than higher up, or lower down. 



THE OPERATION FOR PERMANENT TRACHEOTOMY.— 

 After having selected the spot on which to operate, secure the horse 

 by means of a twitch, reduce the sensibility of the part by injecting 

 cocaine (p. 619), get his head elevated by an assistant, render the 

 skin tense over the part by means of a finger and the thumb of 

 the left hand, make in the middle line of the throat a longitudinal 

 incision of from 2 to 2^ inches in length, through the skin, and 

 insert into the wound a pair of spring retractors to hold the edges 

 of the skin open. On each side of the median line of the windpipe, 

 excise with a narrow but strong scalpel a semicircular piece, out 

 of two rings of the windpipe, after having guarded the resulting 

 circle of cartilage from falling into the windpipe by passing through 

 it a sharply curved needle threaded with wire, which is preferable 

 to a material that might be liable to be cut through, if accidentally 

 touched with the knife. The circular opening should of course 

 be of the same diameter as the body of the tube which is to be 

 inserted. In order to interfere as little as possible with the 

 stability of the windpipe at the site of the operation, it is advis- 

 able to make the opening in the upper portion of one cartilaginous 



