THE TEETH. 



1545 



Fig 



Canine teeth of left side, 

 labial (A) and lateral {B) as- 

 pects. C, temporary canines. 

 (Leidy.) 



from the root and suggests that of an incisor with the angles taken off. The Hngual 

 side of the crown of the upper tooth tends to be convex, often having a ridge running 

 down to the small tubercle at the base. In the lower tooth this side is plane or con- 

 cave, with a distinct tubercle, which exceptionally is enlarged 

 so as to hint at a secondary cusp. The sides of the crown 

 are triangular. The borders of the enamel are convex to 

 the gum on the labial side, less so on the lingual, and slightly 

 concave laterally. The /a/i^- of the upper tooth is the longer 

 and the less compressed ; it very rarely ends in a bifurcation, 

 but this is less uncommon in the lower. The direction of the 

 end of the fang is uncertain. The whole tooth is broader 

 on the labial than on the lingual side. The pulp-cavity is 

 most marked in antero-posterior sections, which show an en- 

 largement of its continuation at the beginning of the root, 

 just beyond the neck. 



The milk canines are much like the second ones, 

 only smaller. The labial surface of the upper tends to divide 

 into an outer and an inner facet. The root is approximately 

 triangular on section, with rounded edges. 



The Bicuspids or Premolars. — These teeth, of which 

 the second is the larger in both jaws, are characterized by 

 crowns with two cusps, one on the buccal and one on the 

 lingual side. The upper ones, being very much the more 

 typical, will be used for the general description. Both the 

 labial and the lingual aspects of the crowns are convex ; they 

 expand laterally from the neck, and each ends in a pointed 

 cusp of which the anterior border is the shorter. This is 

 used in determining the side, but we agree- with Testut that 

 the guide is often useless. The buccal cusp is the larger. The cusps are separated 

 by a furrow from which small ramifications often run onto the buccal one. The lin- 

 gual cusp has an unbroken surface. The buccal* cusp of the first bicuspid is more 

 prominent than the lingual, but in the second they reach the same plane. The bor- 

 der of the enamel is convex towards the root on both the buccal and lingual aspects, 

 the ends of these .curves meeting on the other sides. The fang is compressed with 

 a groove on the sides next its neighbors. That of the second is 

 often bifid just at the tip, but that of the first is very often, per- 

 haps usually, divided into two throughout, having a buccal and 

 a lingual root. Sometimes the former is subdivided, so that it 

 has three like a molar. The root has in general a .backward 

 slant. 



The lower bicuspids have smaller grinding surfaces on 

 the crowns than the upper, but the roots are longer, and the 

 crowns, seen from the side, are at least as large. The first has 

 a well-developed buccal cusp, curving in from the buccal surface, 

 and a very small lingual one connected to the former by a ridge 

 interrupting the fissure between them, which gives the tooth 

 something of the effect of a small canine. The second, like that 

 of the upper jaw, has the two cusps in one plane ; the lingual 

 one is sometimes double, and the plane is often obscure. The 

 flattened fang is but faintly grooved, if at all, and is rarely 

 bifid. 



The pulp-cavity of the bicuspids ends in an expansion below 

 each cusp, that under the buccal being the larger. In the upper 

 teeth the cavity is much compressed from side to side in the 

 root. In the first upper Ijicuspid there are usually two pro- 

 longations to the point of the fang, even when the root is not 

 split. In the second the cavity generally agrees with the conformation of the root. 

 In the lower teeth the cavity is less compressed and is tolerably roomy as it enters 

 the root. It is usually single, but may split. 



First premolar teeth 

 of left side, labial {A) 

 and lateral {B) aspects. 

 (^Leidy.) 



