896 THE DIGESTIVE SYSTEM. 
Of the two margins sloping away from the apex of the crown, the lateral is the longer in both 
teeth. After it has been a little worn the lower canine is less distinetly pointed than the upper ; 
Central incisor Canine 2nd premolar 2nd molar 
' | ) 
| Lateral incisor Ist premolar | Ist molar | 3rd molai 
NI 
\f 
i 
| ; A | | | 
Laterat incisor ™ Ist premolar Ist molar | 3rd molar 
Central incisor Canine 2nd premolar 2nd molar 
Fic. 651.—THr PERMANENT TEETH OF THE RIGHT SIDE, INNER OR LINGUAL ASPECT. 
The upper row shows the upper teeth, the lower row the lower teeth. The cingulum is distinct on the upper 
incisors and both canines, the lingual cusp on the upper lateral incisor and the upper canine. 
its root is also more flattened. On the labial surface of the crown, of both canines and premolars, 
a wide low vertical ridge (labial ridge) can generally be made out (Fig. 650); it is most dis- 
tinct on the canine and first upper premolar. 
Premolar or Bicuspid Teeth ee premolares, Figs. 650 and 651).—Eight in in 
number, two in each jaw above and below, the premolar teeth are placed behind the 
canines, and in front of the molars as indi- 
cated by the term “premolar.” The crown, 
which, unlike that of the incisors and 
canines, 1s flattened from before backwards 
(proximo-distally), is characterised by the 
presence of two cusps (Fig. 652), hence 
the term bicuspid often applied to these 
teeth. One of the cusps, the larger, is 
placed on the outer or labial, the other 
on the inner or lingual side. The labial 
and lingual surfaces are both convex. 
The root is single, but it is, as a rule, 
flattened from before backwards (proximo- 
custally) and grooved, showing in this a 
tendency to division, which often actually 
takes place in the first upper premolar. 
The upper premolars are easily distin- 
Fic, 652.—Tue Upper PERMANENT TrETH, viewed guished by the fact that their two cusps 
POU TION are large and are separated from one 
The cusps of the premolars and molars of the right another by a distinct antero-posterior 
ie af of pcb) ave paliouanly wel shown. fissure (ig, 662); whilst in the lower 
lingual) to the outer posterior (labio-distal) cusp premolars, on the other hand, the separa- 
is also distinct in the first and second molars. tion Waa the two ae 1s not effected 
meer tas, show fou cuts one of by a continuous fissure as in the upper 
Panna * teeth, itt by ‘ge api fie depressions 
separated by a ridge, which joins the two 
cusps (Fig. 653). In the upper premolars, therefore, the two cusps are separated 
by a fissure, in the lower they are united by a ridge. 
The first upper premolar is often slightly larger than the second; the reverse is the case in 
the lower jaw. The outer or labial surface of the crown is usually somewhat larger than the 
