872 



THE ORGANS OF DIGESTION. 



FIG. 469. Right half of upper 

 jaw (from below), with the cor- 

 responding teeth. The letters 

 and numbers point to the 

 classes of teeth and the num- 

 bers in classes. 



The crown is directed almost vertically and is spade-like in form ; it has the form 

 of a truncated cone whose top has been compressed into a sharp horizontal cutting 

 edge. Before being subjected to attrition this edge pre- 

 sents three small elevations. The labial surface is convex, 

 and marked by three longitudinal ridges extending from 

 the edge tubercles toward the neck of the tooth. The 

 lingual surface is concave, and is marked by two marginal 

 ridges extending from an encircling ridge at the neck to 

 the angles of the cutting edge of the tooth. The ridge at 

 the neck is termed the cingulum or basal ridge. 



The mesial and distal surfaces are triangular, the 

 apex of the triangle at the cutting edge. 

 The neck of the tooth is constricted. 

 The root is long, single, and has the form of a trans- 

 versely flattened cone, thicker before than behind. The 

 root may. be curved. 



The incisors of the upper jaw are altogether larger 

 and stronger than those of the lower jaw, the central 

 incisors being larger and flatter than the laterals. They 

 are directed obliquely downward and forward. 



The incisors of the lower jaiv are smaller and flatter 

 than the upper, and the elevations upon their lingual 

 faces are not marked. The two central are smaller than 

 the two lateral incisors, being the smallest of all the 



teeth. The roots of these teeth are flattened laterally. 

 The canine teeth (cuspidati) are four in number, two 

 in the upper, two in the lower jaw one being placed 

 distal to each lateral incisor. They are larger and 

 stronger than the incisors, especially in the roots, which 

 are deeply implanted and cause well-marked prominence 

 of the process at the places of insertion. 



The crown is large, of spear-head, form and its very 

 convex labial surface is marked by three longitudinal 

 ridges. The concave labial surface is also marked by 

 three ridges which unite at a basal ridge. The point or 

 cusp is longer than in the other teeth, and is the point of 

 division between a short mesial and a long distal cutting 

 edge. 



The root is oval or elliptical in transverse section, and 

 is longer and more prominent than the roots of the 

 incisors. 



The upper canines or cuspids (vulgarly called the eye 

 teeth) are larger and longer than the two lower, and 

 in occlusion are distal to them to the extent of half the 

 width of the crown. 



The lower canines (vulgarly called the stomach teeth) 

 have the general form of the upper cuspids, but their lin- 

 gual surfaces are much more flattened', owing to the 



absence of the elevations marking the upper. Their roots are more flattened and 

 may be bifid at their apices. 



The bicuspid teeth (premolars) are eight in number, four in each jaw ; they are 



placed distal to the cuspid teeth, two upon each side. They are double cuspids in form. 



The crown is surmounted by two cusps, one buccal and one lingual, separated 



by a groove, the buccal being more prominent and larger than the lingual. The 



lower bicuspids are not truly bicuspid, the first having but a primitive lingual cusp, the 



second having the lingual cusp divided into two sections i. e. it is usually tricuspid. 



The necks of the teeth are oval ; the roots are laterally compressed, that of the 



FIG. 470. Right half of 

 lower jaw, with the corre- 

 sponding teeth. The letter 

 and numbers point to the 

 various cusps or their modifi- 

 cations on the different teeth 

 (Burchard). 



