10 A MANUAL OF DENTAL ANATOMY. 



The labial surface is slightly convex in each direction, 

 and often presents slight longitudinal depressions, which end 

 at the cutting edge in slight notches. 



In recently-cut teeth the thin cutting edge is elevated 

 into three slight cusps, which soon wear down and disappear 

 after the tooth has been in use. 



The edge of an incisor may be regarded as formed by the 

 bevelling off of the dentine of the lingual surface, which is 

 nearly flat from side to side, with a slight tendency to con- 

 cavity, while from above downwards it is distinctly concave, 

 and often presents longitudinal depressions similar to those 

 on the labial surface. The lingual surface towards the gum 

 terminates in a distinct prominence, oftentimes amounting 

 to a bounding ring of enamel, termed the basal ridye, or, in 

 the language of comparative anatomy, the cingulum. It is 

 variable in the extent of its development ; it rarely rises 

 into a central prominence at the back, but in the angle 

 where the ridges of the two sides meet a deep pit is often 

 left in the enamel, which is a favourite site for caries. The 

 crown, or what amounts to the same thing, the enamel, ter- 

 minates on the lingual and labial aspect of the tooth in a 

 curved line, the convexity of the curve being directed 

 upwards towards the gum; on the insterstitial surfaces, 

 both median and distal, the curve is less regular, and its 

 contour would be more correctly described as V-shaped, the 

 apex of the V being towards the crown of the tooth and 

 away from the gum. ^ The dentist will do well to remember 

 the disposition of the enamel in this situation, as it is a 

 point of some importance in shaping the cervical edge of a 

 cavity preparatory to filling it. 



The transverse indentations of the enamel met with both 



on lingual and labial surfaces, though more especially in the 



latter, are marks of arrest of development, and, common as 



they are, are to be regarded as abnormalities. 



ps The central incisors are larger than the laterals, though 



