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92 EMBRYOLOGY OF THE DENTAL TL'^SUES.
The pcriec'tiicntuni loniis an clastic membrane and acts as a cushion
to lessen the concussion when the teeth come to tion. Its connective-tissue fibers are seen to pass into the cementum,
and within that substance are supposed to be Sharpey's fibers. Where
the cementum is thicker it is rich in cellular structure. The pericemen-
tum, then, connects with the cementum by its fibers; these in turn con-
nect with the branches of the cement corpuscles, through these with the
granular layer of Tomes, and thence on to the fibrils of the dentin.
Nasmyth's Membrane.
Concerning this structure Tomes states that
" lender the name of Nasmyth's membrane, enamel cuticle, or per-
sistent dental capsule, a structure is described about which much differ-
ence of opinion has been, and indeed still is, expressed. Over the
enamel of the crown of human or other mammalian teeth, the crown of
which is not coated by a thick layer of cementum, there is an exceed-
ingly thin membrane, the existence of which can only be demonstrated
by the use of acids, which causes it to become detached from the surface
of the enamel. When thus isolated it is found to form a continuous
transparent sheet, upon which, by staining with nitrate of silver, a
reticulated pattern may be brought out, as though it were made up of
epithelial cells. The inner surface of Nasmyth's membrane is, however,
pitted for the reception of the ends of the enamel prisms, which may
have something to do with this reticulate ajDpearance. It is exceedingly
thin, Kolliker attributing to it a thickness of only one twenty-thousandth
of an inch. But, nevertheless, it is very indestructible, resisting the
action of strong nitric or hydrochloric acid, and only swelling slightly
when boiled in caustic potash. Notwithstanding, however, that it resists
the action of chemicals, it is not so hard as the enamel, and becomes
worn ofiF tolerably speedily, so that, to see it well, a young and unworn
tooth should be selected."
The writer's investigations lead to the inference that the membrane
is nothing more than the layer of cells of the internal epithelium of the
enamel organ, the ameloblasts, which, having performed their function,
have filled with calco-globulin and have partially calcified, becoming
somewhat like that tissue which we find on the borderland of calci-
fication.
It is probable that the lacunse found occupying a fissure between
the cusps of the teeth, in the enamel, are nothing more than a little of
the connective tissue which has become infolded and ossified before
the eruption of the tooth.
92 EMBRYOLOGY OF THE DENTAL TL'^SUES.
The pcriec'tiicntuni loniis an clastic membrane and acts as a cushion
to lessen the concussion when the teeth come to
and within that substance are supposed to be Sharpey's fibers. Where
the cementum is thicker it is rich in cellular structure. The pericemen-
tum, then, connects with the cementum by its fibers; these in turn con-
nect with the branches of the cement corpuscles, through these with the
granular layer of Tomes, and thence on to the fibrils of the dentin.
Nasmyth's Membrane.
Concerning this structure Tomes states that
" lender the name of Nasmyth's membrane, enamel cuticle, or per-
sistent dental capsule, a structure is described about which much differ-
ence of opinion has been, and indeed still is, expressed. Over the
enamel of the crown of human or other mammalian teeth, the crown of
which is not coated by a thick layer of cementum, there is an exceed-
ingly thin membrane, the existence of which can only be demonstrated
by the use of acids, which causes it to become detached from the surface
of the enamel. When thus isolated it is found to form a continuous
transparent sheet, upon which, by staining with nitrate of silver, a
reticulated pattern may be brought out, as though it were made up of
epithelial cells. The inner surface of Nasmyth's membrane is, however,
pitted for the reception of the ends of the enamel prisms, which may
have something to do with this reticulate ajDpearance. It is exceedingly
thin, Kolliker attributing to it a thickness of only one twenty-thousandth
of an inch. But, nevertheless, it is very indestructible, resisting the
action of strong nitric or hydrochloric acid, and only swelling slightly
when boiled in caustic potash. Notwithstanding, however, that it resists
the action of chemicals, it is not so hard as the enamel, and becomes
worn ofiF tolerably speedily, so that, to see it well, a young and unworn
tooth should be selected."
The writer's investigations lead to the inference that the membrane
is nothing more than the layer of cells of the internal epithelium of the
enamel organ, the ameloblasts, which, having performed their function,
have filled with calco-globulin and have partially calcified, becoming
somewhat like that tissue which we find on the borderland of calci-
fication.
It is probable that the lacunse found occupying a fissure between
the cusps of the teeth, in the enamel, are nothing more than a little of
the connective tissue which has become infolded and ossified before
the eruption of the tooth.
