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48 MACROSCOPIC ANATOMY OF THE HUMAN TEETH.
As the roots are usually crooked, the difliculty of euteriuo' thcni is
increased, as the canals follow the form of the roots.
Fourth molars sometimes ai)j)ear as supernumerarv teeth, and are
either fused to the uj)])er tiiird molar in a variety of uncouth forms
(Fig-. 2--shai)ed teeth between the
buccal faces of the second and third molars (h) or at the distal aspect
of the latter tooth. The fourth molar rarely appears as a full molar,
c.\ce])t in some of the large-toothed races, as negroes, Australians, etc.,
and then usually in the lower jaw. Among the negroes in Africa the
fourth molar is sometimes found in full form as a typical molar.
Fig. 29.
•^^- T ' /•
Negro jaw with fourth molar.
The Deciduous Teeth.
IS. The DECIDUOUS TEETH are those which appear in infancy and
serve the purpose of dental organs during the first years of the develo])-
ment of the individual, until the jaws and their environment are ready
for the larger, permanent teeth to come into place. They bear a direct
relationship to the conditions of the digestive apparatus and the food
required at that early stage. The food of infancy being simple and
requiring little mastication, the deciduous set are small and insufficient
for the reduction of more resisting substances. As these foods come to
form part of the dietary, the larger teeth of the permanent set appear,
and perform the duties of higher functional activity.
The crowns of the deciduous teeth resemble, in a general way, those
of the permanent teeth which succeed them, except the deciduous
molars (Fig. 30, a, d), which are very different from the bicuspids
of the permanent set which displace them.
The incisors of both jaws precede the analogous teeth of the same
series of the permanent set. They are similar in form, but reduced {b),
and do not have the main features so characteristically marked. They
are infantile in form and function. T!ie roots of these teeth are
48 MACROSCOPIC ANATOMY OF THE HUMAN TEETH.
As the roots are usually crooked, the difliculty of euteriuo' thcni is
increased, as the canals follow the form of the roots.
Fourth molars sometimes ai)j)ear as supernumerarv teeth, and are
either fused to the uj)])er tiiird molar in a variety of uncouth forms
(Fig-. 2
buccal faces of the second and third molars (h) or at the distal aspect
of the latter tooth. The fourth molar rarely appears as a full molar,
c.\ce])t in some of the large-toothed races, as negroes, Australians, etc.,
and then usually in the lower jaw. Among the negroes in Africa the
fourth molar is sometimes found in full form as a typical molar.
Fig. 29.
•^^- T ' /•
Negro jaw with fourth molar.
The Deciduous Teeth.
IS. The DECIDUOUS TEETH are those which appear in infancy and
serve the purpose of dental organs during the first years of the develo])-
ment of the individual, until the jaws and their environment are ready
for the larger, permanent teeth to come into place. They bear a direct
relationship to the conditions of the digestive apparatus and the food
required at that early stage. The food of infancy being simple and
requiring little mastication, the deciduous set are small and insufficient
for the reduction of more resisting substances. As these foods come to
form part of the dietary, the larger teeth of the permanent set appear,
and perform the duties of higher functional activity.
The crowns of the deciduous teeth resemble, in a general way, those
of the permanent teeth which succeed them, except the deciduous
molars (Fig. 30, a, d), which are very different from the bicuspids
of the permanent set which displace them.
The incisors of both jaws precede the analogous teeth of the same
series of the permanent set. They are similar in form, but reduced {b),
and do not have the main features so characteristically marked. They
are infantile in form and function. T!ie roots of these teeth are
