the modifications in the development of the dental matrix in
different animals and their analogies with those described by the
foregoing authors in the Human Subject and other mammalia are
detailed in the body of the present work.
The dentinal pulp is always the first developed part of the
matrix, and makes its appearance in the form of a papilla, budding
out from the free surface of a fold or groove of the mucous membrane
of the mouth, and generally of that which covers the inner side
of the jaws or their rudiments. In certain fishes, as the shark, the
tooth is completed without the development of the matrix proceeding
beyond this ‘ papillary ’ stage.
The first papilla may be distinctly recognized in the maxillary
mucous groove of a human embryo, one inch in length; the others
quickly follow. By the growth of the contiguous mucous membrane;
the papilla appears to sink into a follicle, and, by the development of
three or four lamellar processes from opposite sides of the mouth of
the follicle, and their mutual cohesion, the papilla is inclosed by a
capsule; this ‘ capsular’ stage of development is completed in the
human foetus at the fifteenth week(l). The capsule is the part of the
matrix destined for the development of the cement. In many fishes
and in serpents, the teeth are completed without the development of
the matrix proceeding beyond this stage.
In those teeth which are defended by enamel, a pulp destined
for its production is developed from the inner surface of the capsule
opposite that to which the dentinal pulp is attached. In the human
subject the enamel-pulp makes its appearance as a soft gelatinous
substance adhering to the opercular plates closing the capsule, and
(l) Goodsir, loc. cit. p. 11.
the adjoining inner surface of the capsule, at the sixteenth week;
the surface of adherence of the 1 enamel-pulp ’ is progressively
extended until it is separated by a mere linear interspace from the
base of the ‘ dentinal pulp.’ “ Whatever eminences or cavities
the one has, the other has the same, but reversed; so that they
are moulded exactly to each other.”(])
With regard to the development of the dentine, Hunter describes
it as an ‘ ossification,’ but without indicating the relation that the
pulp bears to the process. “ As the ossification advances it gradually
surrounds the pulp till the whole is covered by bone, excepting
the under surface; and while the ossification advances, that part
of the pulp which is covered by bone is always more vascular than
the part which is not yet covered. The adhesion of the pulp to the
new-formed tooth or bone is very slight, for it can always be separated
from it without any apparent violence, nor are there any vessels
going from the one to the other; the place, however, where it is
most strongly attached is round the edge of the bony part, which is
the last part formed.” “ Both in the body and in the fang of a
growing tooth, the extreme edge of the ossification is so thin, transparent
and flexible, that it would appear rather to be horny than
bony, very much like the mouth or edge of the shell of a snail when
it is growing ; and, indeed, it would seem to grow much in the same
manner, and the ossified part of a tooth would seem to have much
the same connexion with the pulp as a snail has with its shell.”(2)
Hunter does not explain the nature of this connexion or the mode
of formation of shell | but he has been generally regarded by Physiologists
as having been the author of the theory that the pulp stood to
(l) Hunter, loc. cit. p. 42. (2) Ibid, p. 39, 40.