THE PERMANENT TEETH 



401 



surface presents two mfundibula, anterior and posterior. It slopes obliquely down- 

 ward and outward, so that the buccal edge is prominent and sharp. Its average 

 width, except at each end of the series, is about an inch (ca. 2.5 cm ) The first 

 and last teeth have three roots, the remainder four or three. 



As may be seen in Fig. 342, the individual teeth of the series ynvy in length In the seed- 

 was 6,6 cm. at the anterior end and S.6 cm at the posterfor er^d '"''"'''" '^' *^° ™^'' 



j.„ ^^^ position of the embedded crowns and roots of the last four varies at 

 different ages and m different subjects. Two factors in this variation may be 

 noted. Ail ot these teeth are developed in the posterior part of the body of the 

 maxilla. As gro^vth proceeds the teeth move forward, so that commonly only the 



last three, but sometimes also the third, project into 

 the maxillary sinus. The second cause of variation 

 is the fact that the anterior limit of the maxillary 

 sinus may be at the extremity- of the facial crest, or 

 about an inch beyond it. In the latter case the third 

 tooth projects into the sinus.^ 



The mandibular or lower cheek teeth are im- 

 planted in the rami of the mandible, forming two 

 straight rows which diverge behind. The space be- 

 tween the rows is considerably less than that separat- 

 ing the upper teeth, especially in the middle of the 

 series. The length of the lower teeth is about the 

 same as that of the upper set. Their direction is 



Dentine Cement 

 Enmnel - 



Cement 



Fig. 345. — Froxtai. Sectiox of 



Lower Cheek Tooth of Horse. 



C, Pulp cavity, Infundibulum filled 



with cement. 



Fig 346. — CK(i.ss-.SEfTroN of Lower Cheek Tooth of Horse. 

 Buccal surface to left. 



also similar, but the embedded portions diverge even more, with the exception 

 of the first and second. The long axis of the first is vertical; the remainder 

 project downward and backward in a gradually increasing obliquity. The buc- 

 cal surface has a longitudinal furrow; the last molar has a secondarj' shal- 

 lower furrow in addition. The lingual surface is uneven, but the grooves are 

 not regular; there are usually three on the first and last tooth. The mastic- 

 atory surface is oblique, sloping upward and inward in correspondence with the 

 opposing tooth; thus the lingual edge is prominent. Its average width (except 

 at each end of the series) is somewhat less than three-fourths of an inch (ca. 1.8 cm. ) . 



' The student is advised to amplify these very general statements by the examination of 

 heads of subjects of varying ages. It may also be noted that the position of the septum between 

 the two divisions of the sinus varies much. 

 26 



