The number of these incisors is sometimes eight in the upper
and six in the lower jaw, as in the Sargus Rondeletii and Sar. Sal-
viani; sometimes it is eight in both jaws, as in the Sargus annularis,
Sargus Vetula, and in the well known Sheep’s-head fish of the coasts
of New York (Sargus Ovis). In another species (Sargus rufescens, O.)
there are six incisors in the upper and eight in the lower jaw. In the
Sargus unimaculatus,(\) in which the incisors present the same number,
their cutting margin is notched, as in the teeth of the Glyphisodons.
The incisors are arranged in close and compact order ; in some
species they are placed nearly vertically; in others, more obliquely
in the jaws ; hut they always form an instrument well adapted for
cropping the sea-weed and other marine plants, which constitute the
food of the fishes of the present genus.
In the common Mediterranean species (Sargus Rondeletii), the whole
of the broad alveolar margin of the intermaxillary bones is paved with
rounded molars, similar to each other in form, but becoming larger as
they are placed further back in the mouth: they are arranged in
three rows; those of the innermost row are the largest, those of the
middle row the smallest.
The premandibular pieces of the lower jaw are similarly paved
with two rows of hemispherical molars, those of the inner row being
the largest. In the Sargus unimaculatus there are two rows of molars
in each jaw. In the Sargus Noct, (Ehrenb.), the molars form four rows
in the upper and three in the lower jaw. In the Sheep’s-head fish,
and in the Sargus rufescens, in which the molars are similar in number
to those of the Sargus Rondeletii, the external row present a somewhat
more conical form than the others. In the Puntazzo bream
they are reduced to a single row in each jaw, and are of very small size.
There is a free and constant succession of teeth in the phytipha-
gous Sargues, as in the rest of the Sparoid tribe. At whatever age
the fish may be, foramina will be seen on the outer side of the bases
of the incisors, and external grinders, and on the inner side of the
internal grinders ; and the foramina lead to cavities which contain the
crowns of new teeth in different stages of development. The old
teeth and the alveolar surfaces to which they are anchylosed are disci)
Pi. | fig. 9.
placed by the absorbent process, and their successors become in
their turn anchylosed to the bony plate which, in the progress of
growth, has at length reached the level of the alveolar margin.
A vertical longitudinal section of the incisor of the Sargusf 1)
sufficiently thin to be examined microscopically by transmitted light,
shows that it consists of a central body of compact dentine, composed,
as in the human tooth, of fine, parallel, close-set calcigerous tubes;
and that the crown is covered by a thick layer of a distinct substance
analogous to enamel.
The structure of the external substance is, however, very unlike
that of the true enamel of the human or mammiferous tooth : other
broadly-marked distinctions are at once seen in the continuation of
the pulp-cavity to the apex of the crown, and in the expanded fang
or base of the tooth.
The calcigerous tubes of the ivory, in the body of the tooth, make
a bend when they leave the pulp-cavity, with the convexity turned
towards the apex ; they are then slightly curved in the opposite direction,
and again bend outwards, with the convexity as in the first curve,
thus describing a beautiful sigmoid undulation. At the base of the
tooth the direction of the calcigerous tubes is more transverse, and
the number of undulations is greater. Near the apex the middle bend
is gradually lost, and the tubes as they proceed outwards describe a
simple curve, with the convexity next the apex of the tooth.
The secondary curvatures of the calcigerous tubes are beautifully and
minutely undulatory (a, fig. 2). The main tubes at their commencement
near the base of the conical cavity of the pulp are more irregularly
flexuous, for a short distance than in the body of the tooth. They
send off minute branches throughout their whole course, at very acute
angles, except near their extremities, where the branches bend outwards
and are consequently more readily discerned. The peripheral
extremities of the calcigerous tubes seem to terminate somewhat abruptly
in a clear and apparently structureless space or stratum, which
intervenes between the tubuli of the ivory and those of the enamel.
External to this is an opake stratum, apparently composed of the ex-
(1) PI. 43, fig. 2.
H