18 
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 
Fia. 1.—Diagrammiatic Sections of various forms of 
Teeth. I. Incisor or tusk of Elephant, with pulp- 
cavity persistently open at base. II. Human incisor 
during development, with root imperfectly formed, 
and pulp-cavity widely open at base. III. Completely 
formed huinan incisor, with pulp-cavity contracted to 
a small aperture at the end of the root. IV. Human 
molar, with broad crown and two roots. V. Molar of 
the Ox, with the enamel covering the crown deeply 
folded, and the depressions filled up with cement. The 
surface is worn by use; otherwise the enamel coating 
would be continuous at the top of the ridges. In all 
the figures the enamel is black, the pulp white, the 
dentine represented by horizontal lines, and the cement 
by dots. 
tooth. 
the pulp-cavity, which is 
very different from the 
widely open 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. 1,1V.) 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 
so in old age, it being only 
in consequence of absorption 
and retrocession of the sur- 
rounding alveolar margins. 
Tf, as often happens, their 
surface Wears away in mas- 
tication, it is never renewed. 
The open cavity at the base 
of the imperfectly developed 
tooth (Fig. 1, IL.) causes it 
to resemble the persistent 
condition of the rootless 
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 
