WILLIAMS' OPERATION AGAINST ROARING IN HORSES 353 



invasion comes after the tissues are better protected against 

 microbian invasion than at the time of completion of the 

 operation. A clean, shaved field, sterilized instruments, clean 

 antiseptic solutions, and clean hands are essential to the best 

 results. 



TECHNIQUE.— First Step.— Preparing the Field.— As 

 the field is one not easily cleansed while in the standing posi- 

 tion this step is usually postponed until the horse is down and 

 rolled upon its back. If it is not desired to prolong the dura- 

 tion of the anesthesia it may precede its administration. The 

 space between the angles of the jaws as far forward as the 



Pig. 172 — Longitudinal Section of Larynx. Dark Line Indicates Course of 



the Incision in Williams' Operation. 



A, Vocal Ventricle. B, B, B, Vocal Chord. C, Profile of Ventricle Beneath 



the Arytenoid Cartilage. D, D, Arytenoid Cartilage. E, Epiglottis. 



M, Bezel of Cricoid. 



base of the hyoid bone and overlapping the first ring of the 

 trachea is clipped, shaved and washed clean with mercuric 

 chloride solution 1-500 and then rubbed with alcohol. 



Second Step. — Incising the Skin and Underlying Muscles, 

 — The incision is made in the median line, extending from 

 Adam's apple anteriorly to the first ring of tbe trachea pos- 

 teriorly. Adam's apple in the operating position lies between 

 the jaws a little anterior to its angles. It presents itself as 

 a rounded protuberance that is easily felt with the fingers, 

 but it must not be mistaken for the base of the hyoid bone, 

 located about two inches further forward. 



The incision is at once carried through the subjacent mus- 



