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6 fladtrykte Pigge, hvoraf de to midterste ere de længste
og kunne betragtes som Tænder; desforuden findes paa
Underfladen, henimod den forreste Rand, to stærke, meget
lange, runde Tænder, en paa hver Side af Mundpladernes
ophøiede Sutur, hvilke rage udoverMundaabningen, Fig. 8,d.
Ryggens Hudskelet have vi tidligere omtalt.
Bugens Hudskelet dannes af listeformige, flade
Kalkstykker, der ligesom Ribber, Fig. 4, a, udfylde Rummet
imellem Bugfuren og Armens Rand. Disse Kalkstykker
ere langstrakte, tykkere paa Midten, tyndere mod Randene
og have en skraa Retning indenfra udad, ovenfra nedad.
De ere taglagte saaledes, at den ovenforliggende Plades
tynde Rand dækker lidt af den underliggendes. Fugerne
ere tildels forkalkede, saa at man ogsaa her, nemlig paa
Armenes Bugflade, har en Slags Pantserbeklædning.
Den indre Ende af disse Kalkribber, Fig. 8, b,
støder umiddelbart til en Adambulacralplade, imedens den
ydre frembyder en lidt ophøiet Ledflade, der artikulerer
med de førbeskrevne Randpigges konkave Ledflade. Til
denne ydre Ende, over dens Artikulationsflade, støde
umiddelbart de smaa, aflange Sideplader af Armens Rygskelet,
Fig. 4, c, hvilke kunne betragtes som dorsale Randplader,
der ere placerede i en Række langs Armens Rand og
kunne kun iagttages efter en meget omhyggelig
Præparation. Enhver af disse Randplader bærer en Paxille, hvis
Naale ere temmelig korte. Kalkribbernes indre Flade er
glat og har paa Midten en ophøiet Længdelinie; den ydre
Flade er noget mere ujevn og har paa Midten en rund,
ophøiet Ledflade, der artikulerer med den tidligere
beskrevne midterste Pig paa Armens Bugflade.
Skelettet frembyder intet særdeles mærkeligt.
Ara-bulacralpladernes Tverprocessers ydre Del har en
skefor-mig, konkav Flade, Fig. 4, d, der synes at være
Fæstepunktet for en Muskel, som strækker sig hen over
Ribbernes indre Ende. Adambulacralpladerne ere smaa og
fladtrykte, bære paa den mod Ambulacralfuren vendende Rand
to Pigge, der tidligere ere omtalte, og støde med sin indre
Rand til Kalkribbernes indre Ende.
Ocellærpladen er forholdsvis temmelig stor og har
paa Midten en dyb Fure.
Odontophoren er næsten firkantet, noget fladtrykt;
den øverste Rand, der er kun lidet hvælvet, er noget
bredere end den underste, der har et neppe mærkbart
Indsnit. Den ydre Flade, den som vender til Kropshulheden,
har paa Midten en stærkt fremspringende Kam (Apophyse);
til Siderne af denne er en svag Fordybning, Fig. 11. Den
margin, six flattened spines, of which, the two middle ones
are the longest, and may be considered to be teeth. There
is also found, on the interior surface towards the anterior
margin, two very long, strong, round teeth, placed, one on
each side of the oral plate’s elevated suture, and these
project inwards, over the oral aperture (fig. 8, d).
The abactinal dermal skeleton has already been
spoken of.
The actinal dermal skeleton consists of fillet-formed
flat calcareous pieces, which like ribs (fig. 4, a), occupy
the space between the actinal furrow and the margin of
the ray. These calcareous ossicles are elongate, thick in
the middle, and thinner towards the extremities, and have
a direction, slanting from the interior part outwards, and
from the superior part, downwards. They are imbricate, in
such manner, that the thin margin of the superior plate
covers a small part of the margin of the inferior plate.
The joints are partly calcified, so that, also, in this
situation, we find a description of calcareous armour plating.
The inner extremities of these calcareous ribs (fig.
8, b), butt, immediately, to an adambulacral plate, whilst
the outer extremity, presents a slightly elevated articulatory
surface, which articulates [with the previously described
concave articulatory surface of the marginal spine. To the
outer extremity, above its articulatory surface, the small,
oblong lateral plates of the dorsal skeleton of the ray
closely butt (fig. 4, c), and may be considered to be
dorso-marginal plates, placed in a series along the margin of the
ray; but, they can only be distinguished after a careful
preparatory treatment. Each of these marginal plates
carries a paxilla, whose needles are- rather short. The inner
surface of the calcareous ribs is smooth, and has an
elevated longitudinal rib in the middle. The outer surface is
somewhat more uneven, and has a round elevated
articulatory surface in the middle, which articulates with the
previously described mesial spine on the actinal surface of
the ray.
The skeleton presents nothing particularly noteworthy.
The exterior part of the transverse processes of the
ambulacral plates, has a spoon-shaped concave surface (fig. 4, d),
which appears to be the point of insertion for a muscle
that extends out over the rib’s inner extremities. The
adambulacral plates are small, and flattened, and carry two
spines on the margin facing the ambulacral furrow,
which have already been spoken of, and they butt with
their inner margin, to the inner extremity of the
calcareous ribs.
The ocular plate is, proportionally, rather large, and
has a deep furrow in the middle.
The odontophore is nearly square, and somewhat
flattened. The superior margin, which is only slightly
convex, is somewhat broader than jthe inferior margin, and on
the latter, there is a scarcely perceptible incision. The
exterior surface; the one facing the body cavity; has in the
middle, a strongly prominent ridge (Apophysis). On each
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