58 THE SURGICAL ANATOMY OF THE HORSE 



operation which is attended by great difficulties, particularly during 

 the separation of the gland from the subjacent structures. 



The DircT of Stenson 



This is the excretory duct of the parotid gland. It leaves the gland 

 at its antero-inferior angle, being formed at the inferior portion of 

 the anterior border by the union of three or four of the largest 

 "ductlets" which drain the gland. 



The duct first takes a course inwardly across the inferior aspect 

 of the tendon of insertion of the sterno-maxillaris muscle, and then 

 passes forwards round the digastricus muscle, to become related to 

 the inner face of the internal pterygoid. 



It passes along the maxillary space in company with the sub- 

 maxillary vein beneath which the duct is placed. With this vein 

 and the submaxillary artery, it next curves round the inferior border 

 of the horizontal ramus of the inferior maxillary bone to reach the 

 face, the duct being the most posterior of the three structures, and 

 the artery being placed in front of the vein. 



The three structures named ascend along the anterior border of 

 the masseter muscle, and throughout this part of their course they 

 lie immediately upon the outer aspect of the horizontal ramus. The 

 three structures maintain the same relationship to one another until 

 they reach the inferior border of the depressor labii inferioris 

 muscle, where the artery gives off its inferior labial branch. 

 The corresponding branch of the vein is received by the latter 

 slightly above the point where the inferior labial artery is given 

 off. 



The duct now passes obliquely upwards and forwards beneath 

 the artery and vein, and, running obliquely across the outer aspect 

 of the depressor labii inferioris muscle, it reaches the buccinator. 

 Passing beneath the zygomaticus, it pierces the buccinator from 



