Full resolution (JPEG) - On this page / på denna sida - Sidor ...
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
15
Blærer, der indeslutte Otolither. hvilke ligge, en paa hver
Side af Nerven, netop paa det Sted, hvor Radialmuskelen
insererer sig, førend Nerven skjules af denne. Fig. 30. d>
e, /. Hvor do to Rygnerver ligge imellem Længdeinusklerne
og Huden, afgive de en Mængde temmelig tykke Grene
ikke alene til Muskellaget, men ogsaa til Huden, hvori de
forgrene sig, Fig. 31, anastomosere med hverandre og ende
i Epithellagets Celler, Fig. 32. Foruden disse Hud- og
Muskelgrene sende de ogsaa dels 1, dels 2 Grene til hver
Rygpapille, i hvis Hud de udbrede sig.
Den midterste Radialnerve paa Bugfladen løber
imellem Længdemuskelen og Huden og afgiver Grene til begge,
dog synes Nerveforgreningerne langtfra at være saa rige
paa Bugen, som paa Ryggen.
De to Side-Radialuerver løbe. idet de forlade
Mundskiven, bagtil imellem Radialkarret og Huden. Enhver af
dem afgiver, lidt bagenfor Længdemusklernes Insertion, 1
Gren til den første Høreblære. der ligger omtrent midt paa
Nervestammen, Fig. 30, g, g, og fra nu af. og indtil den
naar den første Fod, sender den 5 Grene til 5 efter
hin-auden liggende Høreblærer. Til første Fod afgiver den en
temmelig tyk Gren. ligesom til en Høreblære. der ligger
ved Foden. I det Rum. som findes imellem 1ste og 2den
Fod, 2den og 3die, 3die og 4de, 4de og 5te. 5te og 6te,
er der to Høreblærer, Fig. 26, c, c, i Rummet mellem de
øvrige Fødder er der kun en Blære. Enhver af disse
Blærer forsynes med en Nervegren, og desforuden er der ved
Grunden af hver Fod en Blære, der ligeledes faar sin Nerve
fra Radialstammen, Fig. 26, d; ialt er der altsaa paa hver
Side 26 Høreblærer. Radialstammen afgiver fremdeles
Grene til Sidepartiets Hud og til Musklerne.
De nævnte Høreblærer ere runde, Fig. 33. a, a, noget
forskjellige i Størrelse; størst ere de to Par. som findes
paa Ryggen, omtr. 0.25""". og mindst ere de. som findes
paa den forreste og bagerste Ende af Kroppen, omtrent
0.06—0.08"». Paa Midten af denne ere de fra 0.16—0.19"".
De dannes af en temmelig fast, hyalin Bindevævsmembran,
Fig. 34, a, der stilkformig forlænger sig hen til
Nerve«tam-men, idet den omfatter Nervegrenen, som gaar til Blæren.
Den indvendige Flade af Blæren er beklædt med et
Epi-thellag, Fig. 34, b. Imellem dette udbreder Nerven sig.
Enhver Blære indeholder en Mængde, dels aflange, dels
runde Otolither, fra 20—130, *Fig. 33. a, 34. c. De runde
ere sammensatte af concentriske Ringe, Tab. II, Fig. 17:
de aflange dannes af Lag, der ligge paa hinanden, og
hvoraf det yderste er det korteste. Fig. 18, a. Paa den
ene Ende af disse Otolither sees hyppigt en liden rundagtig
Freiustaaenhed, Fig. 18, b.
On passing behind the oral disk, they furnish that organ
with several offshoots, which ramify in its integument. The
two radial dorsal nerves branch dichotomously, both
furnishing an offshoot to each of the large vesicles, enclosing
Otoliths. placed one on either side of the nerve, at the exact
point where the radial muscle issues, previous to its
concealing the nerve, fig. 30. d, e, f. The two dorsal nerves,
where they extend between the longitudinal muscles and the
skin, furnish a number of rather thickish branches not only
to the muscular layer, but also to the integument, in which
they ramify, fig. 31. anastomosing one with the other, and
terminating in the cells of the epithelium, fig. 32.
Exclusive of these tegumentary and muscular offshoots,
ramifications proceed to each dorsal papilla, sometimes 1.
sometimes 2, in the skin of which they spread.
The medial radial nerve on the surface of the belly
extends between the longitudinal muscle and the
integument, furnishing both with branches ; the nervous
ramifications. however, would appear to be far less numerous on
the vented than on the dorsal surface.
The two lateral radial nerves take a backward course
from the oral disk, between the radial vessel and the skin.
A little posterior to the point of insertion of the longitudinal
muscles, each of these nerves furnishes a branch to the first
auditory vesicle, placed about midway on the nervous
trunk, fig. 30, g, g; from this point to the first sucker,
it sends forth 5 separate offshoots to as many
successively disposed auditory vesicles. The first sucker, and
an auditory vesicle at its base, are furnished each with
a thickish branch. In the spaces intervening between
the first and second, the second and third, the third
and fourth, the fourth and fifth, and the fifth and sixth,
occur two auditory vesicles, fig. 26, c, c; in the spaces
between the remaining pairs of suckers, only one. Each of
these vesicles is provided with a nervous branchlet; and at
the base of every sucker occurs a vesicle, whose nerve
proceeds from the radial trunk, fig. .26, d; each side has
accordingly, in all, 26 auditory vesicles. Moreover, the
radial trunk also furnishes the lateral portion of the
integument and the muscles with branches.
The auditory vesicles, which are globular in form, fig
33, a, a, vary somewhat in magnitude; the largesj, are the
two pairs on the back, measuring about 0.25"", the smallest,
those at the anterior and posterior extremities of the trunk,
which measure 0.06""—0.08"". In the medial region they are
from 0.16"" to 0.19"" in diameter. They consist of a
comparatively firm, hyaline membrane of connective tissue, fig. 34, a,
which extends as a pedunculate appendage to the nervous
trunk, enclosing the nervous branch that goes to the
vesicle. The inner surface- of the vesicle is covered by an
epithelian layer, fig.- 34, b. Throughout the latter the nerve
spreads. Every vesicle contains a number (20—130) of
Otoliths, part oval and part circular, figs. 33, a; 34. c.
The round Otoliths are built up of concentric rings, the
oval of divers calcareous layers, lying one upon the other,
the outermost layer being the shortest, fig. 18, a. At one
extremity of these Otoliths, is frequently seen a small
roundish prominence, fig. 18, b.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
