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NERVES OF THE PULP. 655
to the lowest portion of the developing enamel organ. Its diiferentia-
tion seems to be controlled by the enamel organ. It is composed at
this early stage of embryoplastic connective-tissne cells, and differs in no
manner, as regards its constituent elements, from the surrounding tissue.
In stained specimens it presents a somewhat darker color, due to the
condensation of the cells which compose it. As we consider it in the
further stages of development there is presented no characteristic which
may not be seen in the surrounding -embryonal connective tissue. Blood-
vessels early show themselves and form numerous anastomosing loops,
which give the papilla a highly vascular nature. The first indication
of the ofiice of the papilla, or pulp, as the formative organ of the den-
tine of the tooth, is seen in the human foetus of four months and the
porcine embryo 8 or 9 cm. in length. There is developed a layer of
cells upon the apical surface of the papilla ; these cells are termed odon-
toblasts. At first they are oval in form and differ very little from the
ordinary connective-tissue cells Mhich make up the princij^al portion of
the papilla. The cells of this outer layer mcmhrana cboris, as it has
been termed — gradually become elongated and send out processes which
connect them with each other and with the cells of the pulp, and also
extend outward toward the inner tunic of the enamel organ. These
latter processes are called the dentinal fibrils. The odontoblasts become
columnar in shape as the time nears for the commencement of their
AYork as dentine-builders. As calcification progresses from the apex of
the papilla new odontoblasts are developed on the sides of the papilla,
until the membrana eboris forms an outer "Covering to the papilla, and
finally the fully-developed pulp. After the dentine is completely cal-
cified the odontoblasts again change their form into oval cells, and con-
tinue to exist as such throughout the life of the pulp. When stimulated
l)y irritation, whether from caries or by thermal changes brought about
by loss of tooth-structure, by attrition, or abrasion, the odontoblasts
again assume their old functional activity and develop secondary
dentine.
While these changes have been going on in the formative outer layer
of the pulp the embryonal connective-tissue cells are developed into
ordinary connective-tissue cells.
Between these fixed connective-tissue cells may be seen the ordinary
plasma-cells noticed throughout the connective-tissue system, the pnlp
being no exception to the rule.
Nerves of the Pulp.
The nerves of the pulp are many and consist of medullated and non-
medu Hated fibres, which enter the pulp through the apical foramen in
various-sized bundles. Passing forward, they break up into smaller
branches and form a rich plexus underneath the odontoblastic layer.
Regarding their termination many speculative theories have been ad-
vanced, but little or no definite knowledge has been presented. Some
assert that the finer fibres pass between the odontoblasts and either unite
with the dentinal fibrils or pass with them into the dentinal tubuli.
Others assert that the non-medullated fibres become united with the
NERVES OF THE PULP. 655
to the lowest portion of the developing enamel organ. Its diiferentia-
tion seems to be controlled by the enamel organ. It is composed at
this early stage of embryoplastic connective-tissne cells, and differs in no
manner, as regards its constituent elements, from the surrounding tissue.
In stained specimens it presents a somewhat darker color, due to the
condensation of the cells which compose it. As we consider it in the
further stages of development there is presented no characteristic which
may not be seen in the surrounding -embryonal connective tissue. Blood-
vessels early show themselves and form numerous anastomosing loops,
which give the papilla a highly vascular nature. The first indication
of the ofiice of the papilla, or pulp, as the formative organ of the den-
tine of the tooth, is seen in the human foetus of four months and the
porcine embryo 8 or 9 cm. in length. There is developed a layer of
cells upon the apical surface of the papilla ; these cells are termed odon-
toblasts. At first they are oval in form and differ very little from the
ordinary connective-tissue cells Mhich make up the princij^al portion of
the papilla. The cells of this outer layer mcmhrana cboris, as it has
been termed — gradually become elongated and send out processes which
connect them with each other and with the cells of the pulp, and also
extend outward toward the inner tunic of the enamel organ. These
latter processes are called the dentinal fibrils. The odontoblasts become
columnar in shape as the time nears for the commencement of their
AYork as dentine-builders. As calcification progresses from the apex of
the papilla new odontoblasts are developed on the sides of the papilla,
until the membrana eboris forms an outer "Covering to the papilla, and
finally the fully-developed pulp. After the dentine is completely cal-
cified the odontoblasts again change their form into oval cells, and con-
tinue to exist as such throughout the life of the pulp. When stimulated
l)y irritation, whether from caries or by thermal changes brought about
by loss of tooth-structure, by attrition, or abrasion, the odontoblasts
again assume their old functional activity and develop secondary
dentine.
While these changes have been going on in the formative outer layer
of the pulp the embryonal connective-tissue cells are developed into
ordinary connective-tissue cells.
Between these fixed connective-tissue cells may be seen the ordinary
plasma-cells noticed throughout the connective-tissue system, the pnlp
being no exception to the rule.
Nerves of the Pulp.
The nerves of the pulp are many and consist of medullated and non-
medu Hated fibres, which enter the pulp through the apical foramen in
various-sized bundles. Passing forward, they break up into smaller
branches and form a rich plexus underneath the odontoblastic layer.
Regarding their termination many speculative theories have been ad-
vanced, but little or no definite knowledge has been presented. Some
assert that the finer fibres pass between the odontoblasts and either unite
with the dentinal fibrils or pass with them into the dentinal tubuli.
Others assert that the non-medullated fibres become united with the
