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OF THE STRUCTURE OF A TOOTH, ETC. 35
part, is found only upon the body of the Tooth, and is there
composed of ordinary dentine, and of the same structure, permeated by
vascular canals (vaso-dentine) : in such instances, the hard unvaseular
dentine is external, and supplies the place of the enamel of higher
The molars of the Dugong afford examples of teeth composed
animals.
of dentine and cement alone, the latter forming a thick crust on the
surface of the former. At first sight, the human teeth and those of
Carnivora might he supposed to consist of but two tissues—dentine and
enamel. This is the statement of the text, and until a comparatively
late period it passed as an acknowledged fact. It was on account of
this apparent simplicity of structure that these teeth were distinguished
as " simple " by the Cuviers. More recent observation, however, has
shown that, besides the enamel and dentine, the third principal dental
tissue—the cement—forms a component part of the human and the
other so-called simple teeth. The teeth of Mammalia, which received
from Cuvier the name of " Compound" or " Complex," differ from those
of Man and the Carnivora only in a different proportion and disposition
of the same constituent tissues. In some instances e.g., the molars of
the Elephant, the molars of the African Wart-hog {Phacoclicerus), the pec-
tinated incisors of the Flying Lemur (Galeopithecus)—a tooth of a high
degree of complexity is produced by the aggregation of distinct denticles.
The great grinding tooth of the Elephant is composed of a series of den-
ticles, each having the form of a plate, vertical to the grinding service,
and transverse to the long diameter of the tooth. Each plate consists
of dentine coated by an investment of enamel, whilst the interspaces
between the denticles are completely filled by cement. In this fully-
formed tooth, the bases of the several divisions of the crown become
fused into a common body of dentine ; but at an earlier period, before
the calcification of the plates is complete, they are held together by the
cement alone. The incisors of Galeopithecus, on the other hand, differ
from the tooth just described in the circumstance that the denticles
project as distinct processes from the base of the crown : each consists
of dentine with a covering of enamel, which is again coated with a layer
of cement of extreme thinness ; at the base the denticles are united, and
into each a prolongation is continued from the common pulp cavity.
But a high degree of complexity of dental structure is not restricted to
Mammalia. In the grinding apparatus of the Parrot-fishes (Scarus), for
instance, which" browse upon the lythophitas that clothe as with a richly-
tinted carpet the bottom of the sea, just as the Ruminant Quadrupeds
crop the herbage of the dry land," (1) dental masses, bearing a close
analogy to the complex molars of the Elephant, are formed by an aggre-
gation of denticles. Moreover, each denticle of the Parrot-fish consists
of dentine with a thick covering of enamel : the denticles are united
(1) Owen, Art. Teeth, Todd's Cyclop. Anat and Phys.
OF THE STRUCTURE OF A TOOTH, ETC. 35
part, is found only upon the body of the Tooth, and is there
composed of ordinary dentine, and of the same structure, permeated by
vascular canals (vaso-dentine) : in such instances, the hard unvaseular
dentine is external, and supplies the place of the enamel of higher
The molars of the Dugong afford examples of teeth composed
animals.
of dentine and cement alone, the latter forming a thick crust on the
surface of the former. At first sight, the human teeth and those of
Carnivora might he supposed to consist of but two tissues—dentine and
enamel. This is the statement of the text, and until a comparatively
late period it passed as an acknowledged fact. It was on account of
this apparent simplicity of structure that these teeth were distinguished
as " simple " by the Cuviers. More recent observation, however, has
shown that, besides the enamel and dentine, the third principal dental
tissue—the cement—forms a component part of the human and the
other so-called simple teeth. The teeth of Mammalia, which received
from Cuvier the name of " Compound" or " Complex," differ from those
of Man and the Carnivora only in a different proportion and disposition
of the same constituent tissues. In some instances e.g., the molars of
the Elephant, the molars of the African Wart-hog {Phacoclicerus), the pec-
tinated incisors of the Flying Lemur (Galeopithecus)—a tooth of a high
degree of complexity is produced by the aggregation of distinct denticles.
The great grinding tooth of the Elephant is composed of a series of den-
ticles, each having the form of a plate, vertical to the grinding service,
and transverse to the long diameter of the tooth. Each plate consists
of dentine coated by an investment of enamel, whilst the interspaces
between the denticles are completely filled by cement. In this fully-
formed tooth, the bases of the several divisions of the crown become
fused into a common body of dentine ; but at an earlier period, before
the calcification of the plates is complete, they are held together by the
cement alone. The incisors of Galeopithecus, on the other hand, differ
from the tooth just described in the circumstance that the denticles
project as distinct processes from the base of the crown : each consists
of dentine with a covering of enamel, which is again coated with a layer
of cement of extreme thinness ; at the base the denticles are united, and
into each a prolongation is continued from the common pulp cavity.
But a high degree of complexity of dental structure is not restricted to
Mammalia. In the grinding apparatus of the Parrot-fishes (Scarus), for
instance, which" browse upon the lythophitas that clothe as with a richly-
tinted carpet the bottom of the sea, just as the Ruminant Quadrupeds
crop the herbage of the dry land," (1) dental masses, bearing a close
analogy to the complex molars of the Elephant, are formed by an aggre-
gation of denticles. Moreover, each denticle of the Parrot-fish consists
of dentine with a thick covering of enamel : the denticles are united
(1) Owen, Art. Teeth, Todd's Cyclop. Anat and Phys.
