PEEMANENT TEETH. 



1119 



nd in 58 per cent, of European, Semitic, and Egyptian skulls ; according to Zuckerkandl, in 

 3'5 per cent, of the lower races and 45'6 per cent, of Europeans.) The third upper molar has three 

 ubercles much more frequently than four amongst Europeans (four only in 36 per cent., although 

 ; t has four more frequently in certain lower races). It should be remarked that, while there 

 ,re practically always four tubercles in the first molar, still there is a tendency to the disappear- 

 \nce of the postero -lingual one, which tendency grows more pronounced as we pass backwards 

 o the second and third molars. The other tubercles are practically constant. 



The three roots of the upper molars (Figs. 881, 882, and 885) are, a large palatine, 

 ubcylindrical in shape, and two labial roots, smaller and flattened from before back- 

 yards. The palatine root, which is placed opposite the posterior labial root, is often united 

 ,;o one of the others. The lower part of the maxillary sinus generally extends down 

 jetween the palatine and the two labial roots (Fig. 879, p. 1113), but the latter project on its 

 loor more frequently than the palatine root. In the last molars the three roots are frequently 

 nore or less united into a single conical process (Fig. 881). 



Lower Molars. The crowns are more massive than those of the upper molars, and are 

 elongated antero-posteriorly (Fig. 884). A crucial groove separates the four chief tubercles from 



Central incisor 



/" /Lateral incisor 



Canine 



1st premolar 



2nd premolar 



1st molar 



FIG. 884. THE LOWER PERMANENT TEETH, VIEWED FROM ABOVE. 



one another ; this bifurcates behind to enclose the fifth, which lies slightly to the labial side 

 )f the middle of the tooth. The number of tubercles present in the lower molars is as follows: 

 The first has usually five (62 per cent, of all races, 61 per cent, of Europeans) ; the second has 

 four, as a rule (five in only 24 per cent, of all skulls) ; the lower dens serotinus has four a little 

 more frequently than five (five in 46 per cent, of all skulls), but like the upper last molar tooth 

 it is extremely variable. 



The roots of the lower molars (Fig. 881), two in number, are flattened from before backwards, 



very wide. The anterior of these has two root-canals ; the posterior but one (Fig. 885). 



The dens serotinus has commonly two roots like its fellows ; occasionally the two are united. In 



determining the side to which a lower molar belongs, it should be remembered that the deep 



part of the root is generally curved backwards, and also that the blunter margin of the crown 



ee above) and the fifth tubercle, if present, are on the labial side. 



Arrangement of the Teeth in the Jaws. The teeth are arranged in each jaw 



in a curved row the arcus dentalis of approximately a semi-oval form (Figs. 



4 and 885). The curve formed by the upper teeth, arcus dentalis superior, 



however, is wider than that formed by the lower set, arcus dentalis inferior, so that 



when the two are brought in contact the upper incisors and canines overlap their 



ellows in front, and the labial tubercles of the upper premolars and molars overlap 



the corresponding ones of the lower teeth (Fig. 886, p. 1120). It will also be 



ien that, as a rule, the teeth in one jaw are not placed exactly opposite their 



fellows, but rather opposite the interval between two teeth, in the other jaw 



