Difference between revisions of "Paper - A Young Human Embryo (Embryo Dobbin) with Head-Process and Prochordal Plate"

From Embryology
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'''Text-Fig. 1.''' Graphic reconstruction of the dorsal view of the embryonic formation; Dobbin embryo X 75.  - Outlines of the embryonal shield (E.s.), yolk-sac (Y.s.) and connecting stalk (c.st.) indicated by a thick line-; outlines of the allantoic canal (ALI = tubular part, AL2 =2: vesicular part) indicated by interrupted lines; outline of the caudal end of the amniotic cavity (Amn.) dotted; cloacal membrane (UL) lined longitudinally where indistinct, cross—hatched where distinct ; P7‘..S‘. =2 primitive streak; chorda process and chorda canal lined transversely; lateral mesodermal bands lined transversely and dotted; ventral openings of the chorda canal marked by arrows on the right, its dorsal opening by an arrow on the left. ++ = HENsEN’s knot ; prochordal plate marked by large dots. On the scale is indicated the level of every fifth section. The median plane is indicated by an arrow.
+
'''Text-Fig. 1.''' Graphic reconstruction of the dorsal view of the embryonic formation; Dobbin embryo X 75.  - Outlines of the embryonal shield (E.s.), yolk-sac (Y.s.) and connecting stalk (c.st.) indicated by a thick line-; outlines of the allantoic canal (ALI = tubular part, AL2 =2: vesicular part) indicated by interrupted lines; outline of the caudal end of the amniotic cavity (Amn.) dotted; cloacal membrane (UL) lined longitudinally where indistinct, cross—hatched where distinct ; P7‘..S‘. =2 primitive streak; chorda process and chorda canal lined transversely; lateral mesodermal bands lined transversely and dotted; ventral openings of the chorda canal marked by arrows on the right, its dorsal opening by an arrow on the left. ++ = HENSEN’s knot ; prochordal plate marked by large dots. On the scale is indicated the level of every fifth section. The median plane is indicated by an arrow.
 +
 
 +
 
 +
'''Text-Fig. 2.''' Graphic reconstruction of the median section through the Dobbin embryo X 7 5. - Ectoderm black; endoderm lined horizontally; primitive streak lined vertically; +=HENSEN’s knot; chorda-process lined obliquely; prochordal plate (Pr.pl.) lined horizontally and dotted; mesoderm dotted; cloacal membrane (O'l.) cross—hatched. Limits of the embryonal shield marked by arrows. AL; 2: proximal (tubular) part of the allantoic canal; Al.2 == its distal (vesicular) part. Hor. —-—=. horizontal plane (the plane of the projection in text-figs. 1 and 8). The caudal part of the embryonic formation, including the cloacal membrane, the allantoic canal, the caudal part of the d amniotic cavity and the connecting stalk are projected into the median plane, and their outlines are marked by interrupted lines. , The cell-layer underneath the intermediate region and the most cranial portion of the head-process, the significance of Which is doubtful, is left White.
 +
 
  
  
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and ends caudally just in front of the connecting stalk.
 
and ends caudally just in front of the connecting stalk.
  
The sections show that the embryonal shield over its cranial two-thirds is not flat
+
The sections show that the embryonal shield over its cranial two-thirds is not flat as is normal at this stage, but is dorsally concave so that in the lateral view of the embryo (fig. 3, Plate 29) the ventral surface of the left half of the embryonal shield is
 +
turned towards the observer and appears much darker than the right half, which is only partly visible.
 +
 
 +
 
 +
The yolk—sac is roughly conical in form; its broad base underlies the embryonal
 +
shield, whilst its apical region narrows to form a spike-like projection. This latter is
 +
prolonged into a filamentous process (about 0 - 88 mm. in length) which exhibits three
 +
enlargements, an elongated thickening close to the apex of the yolk-sac, an oval
 +
swelling near the middle of its length and a quite minute nodule close to its termination
 +
(fig. 3, Plate 29). It ended freely, without reaching the chorion. The entire process
 +
represents the yolk~sac process first described by STRAHL and BENEKE 1910, and
 +
subsequently observed in all adequately preserved early human embryos in a more
 +
or less developed condition. The process attains its maximum development in the
 +
embryos Teacher-Bryce II (BRYCE, 1924) and BENEKE, in which it reaches and is
 +
attached to the opposite wall of the chorion. The latest stage in which it has been
 +
observed in this complete condition is the embryo, Ct POLITZER, with seven pairs of
 +
somites (G.PoLI'rzER, 1930). 
 +
 
 +
 
 +
The yolk-sac at its postero-dorsal extremity is in the sections seen to be continued
 +
into the mesoderm of the connecting stalk in the form of an elongated canal (the
 +
allantoic canal). At its caudal end this enlarges to form a distinct thin-walled vesicle,
 +
which can be seen. both in the dorsal and lateral views of the embryo (figs. 3 and 4,
 +
Plate 29) as a small oval structure on the surface of the connecting stalk close to its
 +
attachment to the mesoderm of the chorion, and on the left side of the same 9 (cf. also
 +
figs. 28 and 29, Plate 32). p , P "
 +
 
 +
 
 +
On the surface of the yolk-sac (fig. 3, Plate 29) a number of vessel—primordia can be
 +
clearly observed.
 +
 
 +
 
 +
In the dorsal view (text-fig. 1 and fig. 4, Plate 29), the shoe—sole shaped form of the
 +
embryonal shield is apparent. Along its middle line the head-process and the primitive
 +
groove could be made out in the intact specimen. The pointed prolongation of the
 +
amniotic cavity along the dorsal surface of the connecting stalk is very distinctly seen
 +
in the dorsal view, whilst the amniotic membrane itself, forming the roof of the amnio-
 +
embryonal vesicle, is seen in the lateral View (fig. 3, Plate 29).
 +
 
 +
==Embryonal Area==
 +
 
 +
(i) H cad-processi‘ and Prockordal Plate;-——In our preliminary note (HILL-FLORIAN,
 +
1931) we distinguished three portions in the axial preblastoporic structures in our
 +
 
 +
* We employ the old term “ head—process ” for the axial formation which extends forwards from
 +
I-IENsEN’s knot, the homologue of the dorsal lip of the blastopore (notopore). This formation comprises
 +
not only the primordium of a part of the mesoderm (which does not seem to be very extensive), but also
 +
that of the chorda, and therefore such terms as “ Mesodermsackchen ” (HERTWIG, 0., 1906) or “ kranialer
 +
Mesoblastfortsatz ” (WALDEYER, 1929) are not suitable.
 +
 
  
  

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Hill, J. P. and Florian, J., 1931. A Young Human Embryo (Embryo Dobbin) with Head-Process and Prochordal Plate. Phil. Tran. Roy. Soc. London B, 219, 443-486.

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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


By J. P. HILL, D.Sc., F.R.S., and J. FLORIAN, M .D.

(From the Department of Anatomy and Embryology, University College, London.)

(Received July 27, 1931.- Read November 19, 1931.)

(Plates 29-35)

Introduction

Our knowledge of the early development of Man has made marked progress during recent years, numerous fairly Well—preserved embryos having been described in greater or less detail. There are still, however, numerous gaps in our knowledge, pertaining not merely to points of detail but to fundamental questions, so that any early embryo reasonably Well preserved and reasonably Well sectioned is deserving of careful study.


Our specimen belongs to the comparatively late presomite stage represented in the literature by such embryos as K113 (GROSSER, 1913), Wa17 (GROSSER, 1931), Peh.1- Hochstetter (ROSSENBECK, 1923), and the embryo of INGALLS (1918), and characterised by the presence of an elongated primitive streak, a luminated chorda-process and a prochordal plate. We offer no apology, however, for presenting a fairly detailed, description of yet another example of this stage, since our embryo amongst other things provides a more complete picture of the cranial region of the head~process than any specimen hitherto described.

History and Treatment of the Specimen

The chorionic vesicle, the embryo of which forms the subject-matter of this paper, was presented to one of us (HILL) by Dr. ROY DOBBIN, of Cairo, through the kind offices of Professor D. E. DERBY. In appreciation of his valuable gift, We have much pleasure in associating Dr. DOBBIN’s name with the embryo.


The clinical history supplied by Dr. DOBBIN is as follows: “ Coitus, 6.10.23 ; effort probably causing abortion, 21.10.23; first bleeding, 22.10.23; abortion (painless), 23.10.23."

Although an abortion, we see no reason to regard the specimen as other than perfectly normal. The chorionic vesicle (which was preserved in spirit) was, when received, somewhat flattened and shrunken (fig. 1, Plate 29). Except over a small area on one side (approximately 3 X 2 mm. in diameter), which was almost bare, the vesicle possessed a fairly uniform covering of short, close~set, branched villi (fig. 2, Plate 29), to which at one point a small fragment of blood—clot adhered. Including the villi, its dimensions in alcohol were as follows : 11 - 5 mm. (in long diameter) X 8 -5 mm. (in short diameter) X 45 mm. (in thickness). After clearing in oil of cedar-wood, the corresponding internal diameters were 9 mm. X 5-5 mm. X 2-5 mm. 2 The vesicle, after being photographed and drawn, was dehydrated and cleared in oil of cedar-wood. A small portion of the chorion, including the bare area, was then carefully removed, and through the opening so made it was possible, fortunately enough, to locate the embryo under the binocular dissecting microscope. The embryo was then isolated along with the segment of the chorion to which it was attached, and stereo-photographs were successfully taken of it, in the cleared condition in oil of cedar—wood. Subsequently Mr. A. K. MAXWELL, with the aid of these photographs and the camera lucida, made the beautiful drawings representing the left lateral and dorsal aspects of the embryo which are reproduced as figs. 3 and 4, Plate 29. These figures are, we believe, unique, in that they are the only illustrations extant of the dorsal andlateral views of the human embryo at this particular phase of development which have been made directly from the embryo itself, and not from models or reconstructions.


The embryo and the related piece of chorion were double—embedded in cedar-wood oil-pyroxelene and paraffin, and cut cranio—caudally by H. BARKER into a complete and really very fine series of sections at 8 (1., the sectional plane being almost exactly transverse to the long axis of the embryo. The state of preservation of the latter proved to be by no means perfect cytologically, but is sufficiently good to ustify us in giving a fairly detailed account of its structural condition. The most obvious fixation—defect is the partial disintegration of the most cranial portion of the Shield-ectoderm, the granular detritus resulting therefrom lying partly in the amniotic cavity and partly below the ectoderm, in a space enclosed between the latter and the detached basement membrane. The fact that the cranial region of the early embryo is the first part to undergo dissolution seems to be Well recognised. Inspection of fig. 3, Plate 29, will show that the embryo no longer occupies its normal position in relation to the chorion, but has been displaced in the ventral direction. Fortunately the deformation accom- panying this displacement has affected only the most caudal part of the embryo and the connecting stalk, and is not of a serious character.


The following measurements were made whilst the embryo was still in oil of cedar- Wood, but must be regarded as approximate only. The lettering refers to text—fig. 2 :-

Anterior margin, embryonal shield to region of cloacal membrane (A-Cl.) 0.98 mm
Vertical diameter (D-F) of yolk-sac 1.092 mm
Antero-posterior diameter of yolk-sac, near its mid-region 0.98 mm
Vertical height, amnio-embryonal vesicle (D-E) 0.468 mm
Length of yolk-sac process 0.88 mm

The measurements of the embryo based on the sections and graphic reconstructions are set forth, along with those of other early embryos, in the tables provided at the end of this paper (p. 480-81).


We take this opportunity of expressing our very grateful thanks to Dr. ROY DOBBIN and to Professor D. E. DERBY for the gift of this interesting embryo. We are further greatly indebted to Professor J. S. B. STOPFORD for the loan of the presomite Manchester embryo, No. 1285 ; to Professor J. C. BRASH for the opportunity of examining the sections of the Thompson-Brash embryo; to Hofrat Professor F. HOCHSTETTER for permission to study the Peh.,-Hochstetter embryo, described by ROSSENBECK, 1923 ; and to Dr. O. BITTMANN, Brno, for the gift to one of us (FLORIAN) of the Bi(ttmann) 24 embryo, to which reference is made on pp. 466—7 . We desire also to thank Mr. A. K. MAXWELL, Artist to the Department, for the care and skill he has expended on the illustrations on Plates 29-34, Which, with the exception of figs. 1 and 2, are all based on photomicrographs; and to Mr. F. J. PITTOCK for his invaluable assistance in photography.

The Embryo as a Whole

The embryonal body, represented by the two vesicles——the amnio-embryonal and yolk—sac vesicles-——-is attached by a very distinct connecting stalk to the chorion (fig. 3, Plate 29). It will be observed that, as has just been mentioned, the dorsal surface of the amnio~embryonal vesicle does not face the chorion, as is the rule in this stage of development, the embryonal shield forming an angle of about 125° with the inner surface of that membrane. This is evidently due to the artificial displacement of the embryonic body, including the connecting stalk, in the ventral direction. At the same time the embryo and the connecting stalk have sufiered a slight rotation round the long axis of the body towards the left side (as may be seen from fig. 4, Plate 29). As is usual at this stage, the yolk—sac vesicle is distinctly larger than the amnio-embryonal.


Text-Fig. 1. Graphic reconstruction of the dorsal view of the embryonic formation; Dobbin embryo X 75. - Outlines of the embryonal shield (E.s.), yolk-sac (Y.s.) and connecting stalk (c.st.) indicated by a thick line-; outlines of the allantoic canal (ALI = tubular part, AL2 =2: vesicular part) indicated by interrupted lines; outline of the caudal end of the amniotic cavity (Amn.) dotted; cloacal membrane (UL) lined longitudinally where indistinct, cross—hatched where distinct ; P7‘..S‘. =2 primitive streak; chorda process and chorda canal lined transversely; lateral mesodermal bands lined transversely and dotted; ventral openings of the chorda canal marked by arrows on the right, its dorsal opening by an arrow on the left. ++ = HENSEN’s knot ; prochordal plate marked by large dots. On the scale is indicated the level of every fifth section. The median plane is indicated by an arrow.


Text-Fig. 2. Graphic reconstruction of the median section through the Dobbin embryo X 7 5. - Ectoderm black; endoderm lined horizontally; primitive streak lined vertically; +=HENSEN’s knot; chorda-process lined obliquely; prochordal plate (Pr.pl.) lined horizontally and dotted; mesoderm dotted; cloacal membrane (O'l.) cross—hatched. Limits of the embryonal shield marked by arrows. AL; 2: proximal (tubular) part of the allantoic canal; Al.2 == its distal (vesicular) part. Hor. —-—=. horizontal plane (the plane of the projection in text-figs. 1 and 8). The caudal part of the embryonic formation, including the cloacal membrane, the allantoic canal, the caudal part of the d amniotic cavity and the connecting stalk are projected into the median plane, and their outlines are marked by interrupted lines. , The cell-layer underneath the intermediate region and the most cranial portion of the head-process, the significance of Which is doubtful, is left White.


The embryonal shield forms in the lateral view (text-fig. 2) an open S-shaped curve. It reaches cranially up to the contour-line formed by the amniotic and yolk—sac vesicles, and ends caudally just in front of the connecting stalk.

The sections show that the embryonal shield over its cranial two-thirds is not flat as is normal at this stage, but is dorsally concave so that in the lateral view of the embryo (fig. 3, Plate 29) the ventral surface of the left half of the embryonal shield is turned towards the observer and appears much darker than the right half, which is only partly visible.


The yolk—sac is roughly conical in form; its broad base underlies the embryonal shield, whilst its apical region narrows to form a spike-like projection. This latter is prolonged into a filamentous process (about 0 - 88 mm. in length) which exhibits three enlargements, an elongated thickening close to the apex of the yolk-sac, an oval swelling near the middle of its length and a quite minute nodule close to its termination (fig. 3, Plate 29). It ended freely, without reaching the chorion. The entire process represents the yolk~sac process first described by STRAHL and BENEKE 1910, and subsequently observed in all adequately preserved early human embryos in a more or less developed condition. The process attains its maximum development in the embryos Teacher-Bryce II (BRYCE, 1924) and BENEKE, in which it reaches and is attached to the opposite wall of the chorion. The latest stage in which it has been observed in this complete condition is the embryo, Ct POLITZER, with seven pairs of somites (G.PoLI'rzER, 1930).


The yolk-sac at its postero-dorsal extremity is in the sections seen to be continued into the mesoderm of the connecting stalk in the form of an elongated canal (the allantoic canal). At its caudal end this enlarges to form a distinct thin-walled vesicle, which can be seen. both in the dorsal and lateral views of the embryo (figs. 3 and 4, Plate 29) as a small oval structure on the surface of the connecting stalk close to its attachment to the mesoderm of the chorion, and on the left side of the same 9 (cf. also figs. 28 and 29, Plate 32). p , P "


On the surface of the yolk-sac (fig. 3, Plate 29) a number of vessel—primordia can be clearly observed.


In the dorsal view (text-fig. 1 and fig. 4, Plate 29), the shoe—sole shaped form of the embryonal shield is apparent. Along its middle line the head-process and the primitive groove could be made out in the intact specimen. The pointed prolongation of the amniotic cavity along the dorsal surface of the connecting stalk is very distinctly seen in the dorsal view, whilst the amniotic membrane itself, forming the roof of the amnio- embryonal vesicle, is seen in the lateral View (fig. 3, Plate 29).

Embryonal Area

(i) H cad-processi‘ and Prockordal Plate;-——In our preliminary note (HILL-FLORIAN, 1931) we distinguished three portions in the axial preblastoporic structures in our

  • We employ the old term “ head—process ” for the axial formation which extends forwards from

I-IENsEN’s knot, the homologue of the dorsal lip of the blastopore (notopore). This formation comprises not only the primordium of a part of the mesoderm (which does not seem to be very extensive), but also that of the chorda, and therefore such terms as “ Mesodermsackchen ” (HERTWIG, 0., 1906) or “ kranialer Mesoblastfortsatz ” (WALDEYER, 1929) are not suitable.


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Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Published December 9, 1931. In Australia copyright has expired - creator died before 1955, provided; work was also published before 1955.


Cite this page: Hill, M.A. (2020, June 2) Embryology Paper - A Young Human Embryo (Embryo Dobbin) with Head-Process and Prochordal Plate. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_A_Young_Human_Embryo_(Embryo_Dobbin)_with_Head-Process_and_Prochordal_Plate

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