82 THE SURGICAL ANATOMY OF THE HORSE 



The animal is now restrained by means of a twitch, and the 

 occipito-atlantal joint is slightly extended by drawing the muzzle 

 forwards. The catheter is then passed along the floor of the nasal 

 chamber to a length which is slightly short of the required distance 

 as indicated. The rounded end of the instrument is now turned 

 outwards, and moved up and down in a vertical plane until the 

 position of the edge of the valve guarding the eustachian orifice can 

 be detected. Under this edge the point of the catheter will pass 

 naturally without much pressure, and if in the eustachian tube, there 

 will be no resistance to its inward passage. 



The point of the tube must still be directed outwards, in order 

 that it may pass readily into the pouch on arriving at the slit by 

 which the latter communicates with the eustachian tube. 



This instrument has been recommended as a means of evacuating 

 the contents of the pouch when of a fluid consistency, but its utility 

 for this purpose is not very effective, since the eustachian tube 

 communicates with the pouch above the level of the floor of the 

 latter. 



H 



YOVERTOBROTOMV. 



For the evacuation of material so accumulated in the poucli, the 

 operation of hyovertobrotomy is performed. The contents are removed 

 by making an incision into the pouch from without. 



From the anatomical description given it will be understood that 

 such an operation entails a considerable amount of care, on account of 

 the various important structures related to the outer aspect of the pouch. 



The operation was first performed in 1779 by Schabert, who 

 gained entrance to the pouch by piercing the stylo-maxillaris muscle. 



Virborg recommends the evacuation of the pouch by making a 

 dependent orifice in the triangle which bears his name. This triangle 

 is bounded by the border of the inferior maxillary bone, the tendon 

 of the sterno-maxillaris, and the submaxillary vein. 



