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Titre : Philosophical transactions of the Royal society of London. Series B, Biological sciences
Titre : Philosophical transactions of the Royal society of London. B
Auteur : Royal society (GB)
Éditeur : printed by Harrison and sons (London)
Éditeur : The Royal society (London)
Date d'édition : 1888-1990
Type : texte,publication en série imprimée
Langue : Anglais
Format : application/pdf
Identifiant : ark:/12148/cb34422226r/date
Identifiant : ISSN 00804622
Source : Bibliothèque nationale de France
Relation : http://catalogue.bnf.fr/ark:/12148/cb34422226r
Description : Variante(s) de titre : Philosophical transactions of the Royal society of London
Description : Variante(s) de titre : Philosophical transactions of the Royal society of London
Description : Périodicité : Irrégulier
Description : Etat de collection : 1888 (vol. 178)-1939
Provenance : bnf.fr
Date de mise en ligne : 13/01/2009
1908 (VOL199).
Page
(Screen 132 / 473)
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124 PROFESSORS J. T. WILSON --AND J. P. IIILL.
Posteriorly the ganglionie plate under considération shows nô definite
Posteriorly the ganglionic plate under considération shows nô definite limitation,
and appears simply to merge in the region of the. first somite,1 If regard were had
only to surface-photographs such as those reproduced in figs..75 and 7G,.it would
nàturally be supposed that that which we here describe as a ganglionic plate in
reality merely "rj&pfesents the forward extension of the paraxial zone of mesoderm.
Fig. 75. is more especially liable to such au Interprétation, inasniuch as the surface-
view can hardly be said to yield any suggestion of the .piesençe of such a sub-
ectodermal ganglionic plate as that described. Here, on each si.ile of the medullary
plate., we find an oblong area boUnded behind by the transverse cleavage-line defiriing
the first distinct somite laterally bya tolerably definite boundary which is. coïncident
with thé inner limit of the pariétal crelomic cavity medially -by the edge of the
.medullary- plate and anteriorly by a well-marked opaque band, parallel with the'
pediclèVf thé acustico-facial ganglion, and skirting the poste rior part of the periphery
of the circulai' auditory plate. Thé broad elongated area so defined is in tolerably,,
obvious séries with the great Trigeminus- plate in front and. also with the acustico-
facial ganglion and its pèdjele. Tirât 'it is not to be interpreted as the forward
̃prolongation of thev.paraxial zone- -6fr:'mêso(|gr^i,f^eyjdeneed iiy the fiict that the
true anterior prolongation of the somitic seiies ̃̃̃itâtîlï ^^X»-isible, in both of the
figures (75 and 76), in the shape of a pointed proïoiigatidii'of. somitic tissue, occupying-
only the medial posterior quarter of the oblohg area ̃ iîi question, and tapering off
hère into a pointed anterior termination. ̃ «t^
Such a négative, of course, in no way involves or supplies a démonstration of thé
ganglionic character of the cellular material of the area in-quèstion.
The .existence of a ganglionic lamina in the sub-ectpdermal plane of the elongated
inteiwal between^fce auditory region and tlîat of the first somite, is rather difBcult
to realise, unless recourse be had.to study of the sections. Thé conception ofthe
existence of such a plate is slightly less ditticult in the case of the right side of
fig. 76. On both sides of the figure, but more especially on the left, the thin and
.imperfect nature of the lamina, except in its anterior and latéral marginal portions,
is revealed in thé relative liglithess jtnd transparenéy of the remainder of thé area
occujûed by the plate. It is owing to this that the ganglionic rudiment seems on
surface-view- of tins sjjecimen to possess the form of an opaqua strand running
] ouUyards and then backwards, behind the auditory region, to fade away in thé
région of the first somite. It has already been pointed out in ^connection with the
èarlv neurular phase that the aj'cuate band of opacity visible in the corresponding
̃situation "in fig. 74: is to be interpreted as thé thickened and convex edge of a
ganglionic plate or lamina.- This thiekened and convex margin is already less sharp
and d( imite m fig 76 than it, was in fig. 74. But in fig.' 75, from Specimen^M,
it is onlv the «uiterior margin of the plate which is clearly defined as such. Thé
liteiaî mai gin, which here runs backwards at right angles with t^e anterior margin,
is now practically coincident with, and on surface-view indistinguishable from, the
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