of their interspaces being nearly transverse to the axis of the skull.
The smaller subsidiary plates are arranged in oblique series internal
to the marginal ones. The base of each plate is hollow, and is
fixed upon a pulp developed from a vascular gum, which is attached
to a broad and shallow depression occupying the whole of the palatal
surface of the maxillary and of the anterior part of the palatine
bones, the Whale being thus, like the Echidna, an example
of a Mammalian animal which may be said to have palatal teeth.
The base of each marginal plate is the smallest of the three sides
of the triangle; it is unequally imbedded in a compact sub-elastic
substance, which is so much deeper on the outer than on the
inner side, as, in the new-born Whale, to include more than one-
half of the outer margin of the baleen-plate. These margins, which
are shown at a, fig. 4, PI. 76, are continued downwards in a
line dropped nearly vertically from the outer border of the jaw ;
the inner margin of each plate(l) slopes obliquely outwards from
the base to the extremity of the preceding margin; the smaller
plates decrease in length to the middle line of the palate, so that
the form of the baleen-clad roof of the mouth is that of a transverse
arch or vault, against which the convex dorsum of the thick
and large tongue(2) is applied when the mouth is closed. Each
plate sends off from its inner and oblique margin the fringe of
moderately stiff but flexible hairs(3), which projects into the mouth.
In a new-born Whale (Baltzna australis) in which the longitudinal
extent of the baleen-matrix was two feet three inches, I found
the number of the large marginal plates to which it gave origin
to be one hundred and ninety. The breadth of the base of each
of the principal plates of baleen was two inches, the length of
the oblique and fringed margin three inches, that of the vertical
external margin three inches and a half, of which two inches were
embedded in the elastic substance or gum. The thickness of the
plate at the free part of this margin is one-tbird of a line, and
the plate becomes a little thinner at the opposite or fringed margin.
The direction of the plates is not quite transverse at every part
of the series ; the inner border is turned rather forwards in the
(1) PI. 76, fig. 4, b. - £2) PI. 76, fig. 4, c. _ (3) PI. 76, fig, 5, c.
anterior and obliquely backwards in the posterior plates, and the
inner margin at the basal part of the posterior plates is slightly
curved towards the back part of the mouth, to which the bristly
terminations of these parts of such plates are directed, thus presenting
an additional obstacle to the escape of the small marine
animals(l), for the prehension and detention of which, this singular
modification of the dental system is especially adapted.
The interspaces of the free extremities of the baleen-plates,
which, from the oblique position of their fringed internal margins,
are only visible by raising the large lip and looking on the outer
part of the series, are in general equal to five or six times the
thickness of the plates themselves; the external line of the plate
is broken by the outward projection(2) of the base of the free
portion of each plate, at least in the dry subject. In the specimen
above alluded to, the pulp-cavity at the base of each principal tooth
presented the form of a narrow, transversely-elongated fissure, from
four to five lines in depth in the larger plates. The bases of the
baleen-plates do not stand far apart from one another, but the
anterior and posterior walls of the pulp-fissure are respectively confluent
with the contiguous divisions of the bases of the adjoining
plates at their thin and extreme margins, which by this confluence
close the basal end of the interspace of the baleen-plates, which
interspace is occupied more than half-way down the plate, by the
cementing substance or gum. Thin layers of horn in like manner
connect the contiguous plates, and may be traced extending in
parallel curves with the basal connecting layer across the cementing
substance, as shown in the diagram, PI. 76, fig. 6, c.
The baleen-pulp (indicated by the dotted line, at a) is situated
in a cavity at the base of the plate, like the pulp of a true tooth;
whilst the external cementing material maintains, both with respect
to this pulp and to the portion of the baleen-plate which it de-
(1) Clio borealis, Limadna, and small pelagic Crustacea. Before the naturalists of the
Arctic expeditions had determined the nature of the food of the true Balance, John Hunter had
stated “ I do suppose the fish they catch are small when compared with the size of the mouth.”
On the Structure and Economy of Whales, Phil. Trans. 1787, p. 397.
(2) The letter a is placed near the line of termination of the baleen matrix in fig. 4, called
the “ bead,” by Hunter, Phil. Trans. 1787, p. 397.