HEAD AND NECK OF THE HORSE 91 



The true roots of the cheek-teeth are short compared with the total 

 length of the teeth, and are generally three in number — one large and 

 medial, and two smaller and lateral. In all, except the first and last of 

 the series, a fourth root may be present. 



In connection with dental operations, it is necessary to observe care- 

 fully the direction of implantation of the maxillary cheek-teeth. 

 When the entire skull rests with the mandible on a horizontal surface, 

 the first tooth is implanted in the jaw with a slope in an upward and 

 forward direction. The next three teeth are implanted practically at 

 right angles to the long axis of the skull ; while the last two slope up- 

 wards and backwards, the slope in the sixth being more pronounced 

 than that of the fifth. It should also be noted that the anterior 

 end of the facial or zygomatic crest is slightly in front of the line of 

 contact of the crowns of the third and fourth teeth. 



Dentine. 



Fig. 34. — Diagram of the chewing surface of a 

 mandibular cheek-tooth. 



The relation of the teeth to the maxillary sinus is also of surgical 

 importance, though this varies at different ages and even in different 

 individuals of the same age. Generally speaking, the last three teeth 

 produce elevations on the floor of the sinus, but it may happen that the 

 third tooth also is associated with the sinus if this cavity is continued 

 farther forwards than usual. The relation of the teeth to the sinus will 

 form the subject of inquiry for the dissector when he is examining the 

 interior of the cavity at a later stage. 



Though the mandibular cheel'-teefh are, on the whole, about as Ions: 

 as the maxillary, their transverse measurement is much less, and conse- 

 quently they have oblong instead of approximately square chewing sur- 

 faces. On the buccal surface of the first five teeth there is a longitudinal 

 groove : on the last tooth there are two grooves. The lingual surface is 

 irregularly grooved longitudinally. The exposed part of the crown is 

 taller on the inner or lingual side, with the result that, as in the 

 maxillary teeth, the chewing surface is set obliquely to the longitudinal 



