i8 



GENERAL ANATOMICAL CHARACTERS 



having at its extremity a minute perforation, through which the 

 vessels and nerves required to maintain the vitality of the tooth enter 



the pulp -cavity, which is 

 very different 

 widely open 



from the 

 cavity at 



the base of the growing 

 tooth. When the crown 

 of the tooth is broad and 

 complex in character, in- 

 stead of having a single root, 

 it may be supported by 

 two or more roots, each of 

 which is implanted in a 

 distinct alveolar recess or 

 socket, and to the apex of 

 which a branch of the com- 

 mon pulp-cavity is continued 

 (Fig. 1, IV.) Such teeth are 

 called "rooted teeth." When 

 they have once attained their 

 position in the jaw, with the 

 neck a little way above the 

 level of the free margin of 

 the alveolus, and embraced 

 by the gum or tough fibro- 

 vascular membrane covering 

 the alveolar border, and hav- 

 ing the root fully formed, 

 they can never increase in 

 length or alter their posi- 

 tion ; if they appear to do 



Fio. 1. Diagrammatic Sections of various forms of SO in old age, it being Only 



_.3th. i. incisor or tusk of Elephant, with pulp- in consequence of absorption 



cavity persistently open at base. II. Human incisor d retrocession o f tne SUr - 

 during development, with root imperfectly formed, . 



Teeth, 



a smaii aperture at tne end 01 tne root. iv. Human r 



molar, with broad crown and two roots. V. Molar of S 



the Ox, with the enamel covering the crown deeply tication, it is never renewed. 



folded, and the depressions filled up with cement. The T'he Ot)6n cavitv at the base 



surface is worn by use ; otherwise the enamel coating < i 1 J i J 



would be continuous at the top of the ridges, in all of the imperfectly developed 



the figures the enamel is black, the pulp white, the tooth (Fig. 1, II.) CaUSBS it 

 dentine represented by horizontal lines, and the cement tQ resemble tne persistent 



condition of the rootless 



tooth. The latter is therefore a more primitive condition, the 

 formation of the root being a completion of the process of tooth 

 development. Functionally it is, however, difficult to say that the 



