io6 THE SURGICAL ANATOMY OF THE HORSE 



into the frontal sinus in order that its contents may be evacuated. 

 This latter opening should be made near the lower limit of the 

 sinus. 



With regard to this point it may be of utility to refer to the 

 seats of operation recommended by Siedamgrotzky and Craig, in 

 the performance of the operation generally. The former " opens the 

 frontal sinus about one-half to three-quarters of an inch in front" 

 {I.e., below if the head be held with its long axis disposed vertically) 

 " of a horizontal line drawn between the two inner angles of the 

 eye, and one and a quarter to one and a half inches from the middle 

 line of the face. After washing out the sinus cavity, he effects a 

 communication between it and that of the nose by thrusting a 

 director downwards and inwards at the deepest spot, breaking through 

 the thin plate of bone and the mucous membrane covering it, and 

 enlarging the opening so made by excising with a tenatome an oval 

 fragment three-quarters of an inch long, and three-eighths of an inch 

 wide." The latter states that the " position in which trephining 

 may be performed on the frontal sinus is near to its lower extremity. 

 The point of operation is about two and a half inches below the 

 nasal canthus, and one inch in front of a line drawn from that 

 canthus to the side of the nasal peak." 



Since both these seats are near the lower limit of the sinus, in 

 such cases as have been referred to where the operator fails to obtain 

 communication between the frontal and superior maxillary sinuses, 

 the adoption of one or other of these seats as outlets through which 

 the contents of the frontal sinus may be driven by irrigation through 

 the higher opening described, will doubtless prove a very potent 

 method of bringing about the desired effect. 



Trephining into the Inferior Maxillary Sinus. — This operation is 

 performed when the condition of empyema affects the inferior 

 maxillary sinus in addition to those before mentioned. There is no 

 natural direct communication between this and the other sinuses, 



