THE PERMANENT TEETH 401 
surface presents two infundibula, anterior and posterior. It slopes obliquely down- 
ward and outward, so that the buccal edge is prominent and sharp. 
width, except at each end of the series, is about an inch (ca. 
and last teeth have three roots, the remainder four or three. 
Its average 
2.5 em.). The first 
As may be seen in Fig. 342, the individual teeth of the series vary in length. In the speci- 
men from which the photograph was taken the lengths of the upper teeth in centimeters enumer- 
ated from before backward were: 6.3, 7.7, 8.5, 8.0, 8.8, 8.2. The distance between the two rows 
was 6.6 cm. at the anterior end and 8.6 cm. at the posterior end. 
The position of the embedded crowns and roots of the last four varies at 
different ages and in different subjects. 
noted. 
maxilla. 
Two factors in this variation may be 
All of these teeth are developed in the posterior part of the body of the 
As growth proceeds the teeth move forward, so that commonly only the 
last three, but sometimes also the third, project into 
Dentine Cement 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.1 
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 
Cement 
———— 
Cement 
Enamel 
Dentine — 
lL 
wa 
( 
NU 
Fig. 345.—Fronrat Srcrion or 
Lower CHeexk Toorn or Horse. 
C, Pulp cavity. Infundibulum filled 
with cement. 
Fic 346.—Cross-secTIOoN oF LoweR CHEEK ToorH oF Horse. 
Buceal 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 secondary 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.). 
1 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 
