1120 



DIGESTIVE SYSTEM 



characteristic chisel shape. The masticating surface is narrow and chisel-edged. 

 In recently erupted teeth, the cutting edge is elevated into three small cusps, 

 which soon wear down, leaving a straight edge. These cusps correspond to three 

 indistinct ridges on the labial surfaces. The lateral angle of the crown is usually 

 more rounded than the medial. The labial surfaces are slightly convex, the lin- 



FiG. 874. 



-Cross-Section of the Medial Upper Incisor, in Situ. 



Atlas.) 



X 4. (From Toldt's 



Dentine of root of tooth 



Root canal of tooth 



Cementum 



Alveolar periosteum 



Wall of dental alveolus 



Marrow spaces of alveolar 

 process of maxilla 



gual slightly concave. The contact surfaces are somewhat triangular. The 7-oots 

 of the incisors are single, though often longitudinally grooved, indicating traces of 

 a division. They are somewhat conical, but flattened from side to side, expecially 

 the lower set, and are slightly curved lateralward. 



The upper or maxillary incisors are much larger than the lower. They are lodged in the 

 premaxilla, and are inclined downward and forward. They overlap the lower incisors in masti- 

 cation, hence the masticating surface is worn off and rounded at its posterior edge, while the 

 anterior edge becomes sharp and chisel-hke. The lingual surfaces of the crowns terminate 

 near the gum in a low, inverted V-shaped ridge, the basal ridge or cingulum. At the ape.x of 



Fig. 875. — Variations in the Form of the Upper Third Molar. (Broomelland Fischelis.) 



the V, near the gum, tliore is often (especially on the lateral incisor) a small lingual cusp. The 

 n.edial u[)p('r irx-isor is distiiiguishod from the lateral by its much larger size. 



The lower (jr mandibular incisors are smaller than the upi)er, the cutting edges being only 

 about half as wid(!. liciiig overlapped by the; ui)per set, the lower incisors have the masti- 

 cating surface worn off anteriorly, leaving a sharj) cutting edge posteriorly. The lower incisors 

 are vertically placed, and the crown becomes narrower toward the neck. A cingulum is rarely 

 visible. The medial lower incisor, unlike the upper, is slightly smaller than the lateral. 



The canines.— (Figs. 868, 809, 870, 871.) The canine teeth [dentes canini] 

 so-called from their prominence in th(! dog-tribe, are tiie longest of all the teeth 

 (fig. 8()8). Th(! crown is thicker and mor(; conical than in the incisors. The 7nas- 

 ticatiny siu-face forms a median angular poi nt, on eitiior side of which the cutting 



