DISEASES OF THE. FACIAL SINUSES. 



.619 



nose, as the' fangs of the molar teeth are then long, and their 

 alveoli fill up the sinus, whereas in the old horse the sinus will. 



Fio. 110, — Skull cut open to show the situation of bony partition of! 

 superior maxillary sinus. The white circle is the Bjxit selected for tre. : 

 phining both cavities by one opening, a. Space between fourth and fifth' 

 molar teeth ; b, Termination of zygomatic spine. 



extend as low as the zygomatic crest, where the opening can h€»l 

 made without danger of coming in contact with the teeth. 



In some instances the frontul sinus has to be opened, especially! 

 when the contained pus is inspissated, and lodged in the convolu- 

 tions of the ethmoidal and turbinated bones ; but in the majority | 

 of instances one opening, at the most depending part of the cavity,' 

 is suflScient. 



The external portion of the maxillary sinus is divided into 

 two compartments by a transverse plate, marked in the drawing, 

 which in many cases is perfect throughout life. The superior 

 portion contains the alveoli of the two last molar teeth, the 

 inferior portion the alveoli of the tliird and fourth, while the 

 first and second molars are quite superficially situated ; very 

 often, indeed, their fangs actually protrude through the maxil- 

 lary bone, or they may be so thinly covered by it that they can 

 be both seen and felt tlirough the skin of a well-bred horse. 

 From this short description it will be seen that the guide to the 

 operator in making the opening through the boi\,e, so as to em- 

 brace both cavities, will be the space between the fourth and fifth. 

 molar teeth. Of this he must judge by an inspection of tha, 



