230 THE TEETH. 



The superior central incisors are the longest of all the 

 front teeth except the canine, being found to have an aver- 

 age measurement in length of about twelve lines; while 

 the inferior central incisors are but ten lines long, and are 

 the shortest of all the teeth. The relative length of the 

 crown and root, though subject to variation, is nearly equal 

 in the upper central incisors, while in the inferior central 

 incisors four lines are assigned to the crown and six to the 

 root. For the lateral incisors of both jaws, four lines and 

 a half for the crown and seven for .the root are regarded as 

 the fair relative average length. The anterior surface of 

 the central incisors is frequently marked by longitudinal 

 ridges, which in early life are found to terminate in small 

 cusps upon the cutting edge of these teeth three of these 

 cusps are seen on the central, and but one on the lateral in- 

 cisor. This serrated provision in the incisors is believed to 

 be nicely adapted to the division of the food, and designed 

 to compensate for the weak condition of the dental system 

 and its muscular powers at this early period. As the per- 

 manent teeth advance these cusps disappear. 



On the posterior surface of the superior central incisors, 

 which have been stated to be concave, and receive the 

 crowns of the lower incisors at an acute angle, raised un- 

 dulations are described to exist in early life, and are re- 

 garded as assisting in the mastication of the food at this 

 time, when the molars are imperfect. 



Professor Harris describes four surfaces to the crown of 

 an incisor, which he thus characterizes: two approxirnal, 

 one labial, and one palatine or lingual surface; also four 

 angles, a right and left labio-approximal, and right and 

 left palato-approximal, or lingua-approximal. 



Canine, or Guspidati (cuspis, a point.) The canine teeth 

 are two in each jaw, and situated one upon either side of 

 the lateral, and with the incisors complete the range of 

 what are called the oral teeth. They particularly distin- 

 guish the carniverous animals, and are designed to tear 

 and rend the food, whilst the incisors simply cut. The 

 crown is conical, and has its anterior surface more con- 



