supporting process of gum is represented at Plate 44, fig. 5; d is
the superficial calcified layer of the pulp c, the hase of which is sunk
into a fossa, or open oapsule of the gum b ; d is the nerve entering
the base of the pulp. In figure 6, PI. 44, the course of the branches
of the fifth pair of nerves, through the permandibular bone of the
pike, to supply the pulps of the teeth, is shown; the size of the
dental nerve hears relation to the vascular and organized texture of
the tooth, and to the rapidity of its growth.
Retzius’ accurate description of the microscopic structure of the
tooth of the Pike {Esox Lucius, L.) is as follows. “ It Consists of an
internal part or nucleus with coarse tubes, and an outer thinner part,
with fine and parallel tubes, which form the covering of the nucleus.
The coarse main-tubes, which occupy the internal and imperfectly
developed parts of the ivory, present at their widest part a diameter of
about 9®th of an inch. ^Their course is almost parallel with each
other and with the axis of the tooth,- and they unite by numerous
larger or smaller anastomoses. Near the basis of the anchylosed
teeth, the larger oblique anastomoses are so near together that their
interspaces are scarce equal to the diameter of the larger tubes. In
recent teeth these tubes contain a blood-red substance, which might
be regarded as a complex pulp. Beautifully minute and very short
tubules of from to j^ th of an inch in diameter, proceed mostly
in a transverse direction from the larger tubes ; and subdivide, as
they proceed, into groups of finer tubes, which form innumerable reticular
anastomoses with each other, and thus fill up the interspaces of
the larger canals. The boundary between the central and peripheral
substances is well defined, and is formed by anastomoses of the exterior
longitudinal bent coarse tubes ; beyond which no coarse tube
extends, but only a series of fine and parallel tubes ; these tubes
manifest the same direction as those in the thin and hollow shell of
the incompletely formed teeth of the higher organized animals: i. e.
the fine tubes that are nearest the apex of the tooth, are almost parallel
with the axis of the tooth, while those which are nearest the root,
proceed transversely to the axis. They soon divide into pencils of
finer branches, which mutually and reticularly anastomose, and give
off at their peripheral extremities close-set parallel tubes, from ^ to
^ t h of an inch in diameter, in which I could perceive neither
branches, anastomoses nor cells. The exterior ivory-like substance
viewed in a section of a Pike’s tooth by a low magnifying power resembles
a layer of enamel. It is extremely thin where it commences
near the base of the tooth, and is thicker at the apex where the fine
branches of the tubes exhibit the most beautiful dendritic arrangement.
The central substance of the tooth is grey in recent teeth,
and yellowish in dried specimens ; the peripheral substance is of the
purest white, and is much harder and more compact than the central
substance. So hard, indeed, is it in dried teeth, that I supposed it
might be covered with an extremely thin layer of enamel, but I could
not by means of the microscope discover any such layer.”
CLUPEOIDS.
54. The Clupeoid family of Fishes, of which the Herring is the
type, is interesting in relation to the dental anatomy of the class on
account of the examples which it offers of very general and extensive
distribution of teeth over the hones which surround the oral cavity,
and of the unusual share which the superior maxillary bones, from
their relative position and development, take in supporting the
teeth of the upper jaw. The different genera, however, of the
Clupeoid, as of other natural groups of fishes, present very diversified
conditions of the dental system ; the almost edentulous Clupano-
don, and the rapacious Erythrinus or the gigantic Sudis, offering the
extremes of these modifications.
In the Clupanodon an almost imperceptible coating of the finest
villiform teeth, upon the pharyngeal hones, forms the sole trace of a
dental system.
The Herring (Clupea Harengus) has very minute sharp-pointed
teeth on the jaws and tongue.
The Pristigaster presents similar teeth on the large intermaxilla-
ries, on a small part of the superior maxillaries, and upon the hyoid,
palatine, vomerine and pterygoid bones.
The little Anchovy, the type of the genus Engraulis, is a good
example of that higher development and allocation of the superior
maxillary hones, which is so rare in the class of fishes; they here