164 ANIMAL DENTISTRY. 



finger pressed against the cheek opposite the decayed tooth, 

 and from the bulge thus made in the cheek externally a 

 measurement is made upward to a point indicated by the 

 animal's age. In the young horse a slight variation must be 

 made for the backward direction of the fifth molar. The sixth 

 molar in young animals is reflected backward beneath the 

 eye and cannot be satisfactorily repulsed. 



For the inferior molars the openings are made at the 

 very border of the jaw in every case except for the fifth and 

 sixth, in which instance it is made upon the most prominent 

 part of the tumefaction caused by the diseased process. For 

 the third, fourth and fifth inferior molars, due allowance 

 must be made for the marked backward direction of their 

 fangs. (See Fig. 115.) 



The openings must be made with due deference for the 

 following important structures : 

 (i) Steno's duct. 



(2) Lachrymal canal. 



(3) Glossofacial artery and vein. 



(4) Superior dental canal and contents. 



(5) Inferior dental canal and contents. 



(6) Superior maxillary division of the trifacial nerve 



near its exit from the skull. 



In the repulsion of the superior teeth complicated with 

 catarrh a single additional opening is made to drain the fron- 

 tal sinus and to give free access to the maxillary sinus, as 

 well as to drain the frontal sinus into the nasal fossa. This 

 opening is located in an oblique direction downward and in- 

 ward four centimeters from the nasal canthus. (See Fig. 

 151) 



Opening the Skull:— This step of the operation requires 

 the consecutive dissection of (i) the skin, (2) the subcutane- 

 ous areolar tissue and muscles, (3) the periosteum, (4) the 

 bone, and (5) the mucous membrane. 



