THE TEETH. 967 
Incisor Teeth (dentes incisivi, Figs. 650 and 651).—These teeth, four in number 
in each jaw, are used specially for cutting the food, hence their name. The crown 
of each is chisel-shaped, and presents an anterior or labial surface which is convex 
in all directions, a posterior concave surface, and a chisel-like edge, which, when 
first cut, is surmounted by three small tubercles separated by two grooves. These 
tubercles, however, are soon worn down, and the edge becomes straight or nearly 
so. Owing to the fact that the upper incisors overlap those in the lower jaw, the 
cutting edge is worn away, or bevelled, on the posterior aspect in the former, but 
on the anterior aspect or summit in the latter. The upper, but particularly the 
upper central incisors, are of large size, and slope somewhat forwards; whilst the 
' 2nd molar 2nd premolar Canine Central incisor 
1 
Ist molar | Ist premolar 
3rd molar 
Lateral incisor 
| 
i} 
Lateral incisor | 
2nd molar 2nd premolar Canine Central incisor 
3rd molar | Ist inolar | Ist premolar 
Fic. 650.—THE PERMANENT TEETH OF THE RIGHT SIDE, OUTER OR LABIAL ASPECT. 
The upper row shows the upper teeth, the lower row the lower teeth. The wide vertical “labial ridge” is 
distinct on the upper canine and premolar teeth. 
lower incisors, which are all nearly equal in size, are much smaller—being the 
smallest of all the teeth—and are placed vertically. The roots of the incisors are 
single, though a groove is occasionally seen on each side, suggesting a division. 
The central upper incisors are very much larger than the upper lateral incisors (Fig. 650), but in 
the lower jaw the opposite is the case, the lateral incisors being slightly the larger. In all incisors 
the outer (distal) angle of the crown is more rounded than the proximal. The posterior concave 
surface of the crown in the upper incisors is usually limited towards the gum by a A-shaped 
ridge (Fig. 651), known as the basal ridge or cingulum. The two limbs of the A are continued 
up along the sides of the posterior surface, whilst the apex is turned towards the gum ; and here, 
particularly in the lateral incisor, there is often developed a small lingual cusp (Fig. 651). The 
cingulum is rarely found on the lower incisors. 
The roots of the upper incisors and canines are conical and rounded (the laterals and canines 
not so distinctly as the centrals, Fig. 654), whilst those of the lower jaw are flattened from side to 
side (proximo-distally). 
Canine Teeth.—In the four canine teeth (dentes canini), which succeed the 
incisors in each row (Figs. 650 and 651), the crown is large and conical, corresponding 
closely in general form to a very large central incisor with its angles cut away, 
so that the crown assumes a pointed or conical shape. The labial surface is 
convex, the lingual usually somewhat concave. The root is single and long, par- 
ticularly in the upper canine, the root of which is longer than that of any other 
tooth, and produces the canine eminence on the anterior surface of the upper jaw. 
The upper canines are larger than the corresponding lower teeth, behind which 
they bite; and they are sometimes known as the “eye teeth.” 
The upper canine presents on its lingual surface a well-marked cingulum, and often a distinct 
lingual cusp ; in addition, there is usually a median ridge running from the point of the crown 
to the apex of the cingulum, which is separated from the lateral part of the cimgulum on each 
side by a slight depression. These points are neither so well marked, nor so constant, in the 
lower as in the upper canine. 
