tulous ; there is a band of villiform teeth on each intermaxillary and
premandibular bone.
lh e Helostomes{ 1) are remarkable for the small size and shape of
their mouth, which resembles the head of a nail driven into the
muzzle, whence their generic name ; their teeth are not less extraordinary,
being attached solely to the inside of the lips, and moving
with them ; they may he regarded, in fact, as a row of slightly calcified
labial ciliiform papillae. The palatines and vomer are edentulous ;
the posterior and inferior pharyngeals support small conical teeth.
In the genera Culisa, Macropodus and Trichopus, the teeth are
attached to the jaws, but are very small or villiform ; the anterior
maxillary teeth in the Gourami (Osphromenus), are a little longer
than the rest. The Spirobranchus is the only genus among those with
labryrinthiform pharyngeals which has palatal teeth. These are
short, coarse and villiform ; there are similar teeth on the vomer,
intermaxillary and premandibular bones ; the side teeth in the latter
locality are longer than the rest.
44. The fishes of the family called Theuties, by Cuvier, have a
small mouth, with a single row of teeth on the intermaxillary and premandibular
bones ; the palate and vomer are edentulous.
The jaw-teeth of the Axinurus are extremely slender ; those of the
Naseus are simply conical and sharp-pointed.
In the genera Prionurus, Priodon, Amphacanthus and Acanthurus,
the teeth are commonly notched or serrate at the margins. Mr. André
has given an accurate magnified view of the external form of the teeth of
the Acanthurus nigricans, (Chætodon nigricans of Linnæus), in the Philosophical
Transactions, and had recognized the arborescent medullary
canals in the body of the tooth, “ through which,” he says, “ the
blood-vessels ramify, which are destined for its growth and nourishment.”
He very justly observes, that a fish having teeth of a crystalline
hardness, and arranged in a single row, cannot he naturally
associated with the Chsetodonts, which are characterized by numerous
rows of flexible teeth, of a totally different form.
The medullary canals in the maxillary teeth of the Acanthurus
nigricans are directly continued from a conical pulp-cavity at the
(1) ij\o£, a nail ; ^ a , a mouth.
base of the tooth, and are occupied, not by blood-vessels only, but
by processes of the organized medulla or pulp, including the nutrient
vessels, nerves, and connecting tissue. The diameter of the medullary
canals at their origin is ^ th of an inch, and their interspaces equal
from four to six of these diameters ; their general course is parallel
to each other and to the axis of the tooth; but they begin to send
off side-branches soon after their origin, and continue to ramify
abundantly throughout their course. The ramifications anastomose
and form arches, of which the convexity is directed towards the
margin of the tooth. Both the main canals and their branches
gradually diminish in size as they approach the margins. The cal-
cigerous tubes, which are every where continued from the medullary
canals, are of extreme tenuity ; the marginal ones, which have a
direct course perpendicular to the surface of the tooth, do not
exceed ^ t h of an inch in diameter. A diminished view of four of
the teeth of the Acanthurus nigricans, as seen with a magnifying
power of sixty linear dimensions, is given in PI. 44, fig. 1. The
imbricated disposition of the teeth is here shewn.
CHiETODONTS.(l)
45. The name of this family of fishes is significative of the peculiar
form of the maxillary teeth, which resemble the hairs of a fine brush,
and are of a soft subtransparent flexible texture, in the majority of
the genera composing it. The pulp-cavity is continued to near the
apex of these slender elongated denticles.(2) The true Chsetodonts
thus characterized, have no teeth on the palatine, vomerine or lingual
bones.
In the genus Chcetodon proper, the setiform teeth are longer than
in the genera Heniochus or Phelmon, in the latter of which they
resemble rather the pile of velvet. In the genus Zanclus the setiform
maxillary teeth are directed forwards.
In the Holacanthus, the setiform teeth are finely pointed ; but in
Platax, (3) the outer row have their extremities compressed, slightly
expanded and terminated by three pointed lobes.
(1) xaLrr), a bristle j oSag, a tooth. PI. 1, fig. 2 (2) PI. 44, fig. 3, a and b. (3) PI. 1, fig. 2, a.