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=External Features of an Early Human Embryo with a Distended Amnion=
 
=External Features of an Early Human Embryo with a Distended Amnion=
  
EXTERNAL FEATURES OF AN EARLY HUMAN EMBRYO WITH
+
By C. J. PATTEN, Sc.
A DL‘TENDED AMNION. By C. J. PATTEN, Sc.]).
 
  
 
(Read before the Anatomical Society of Great Britain and Ireland, at Birniingham, 26th June 1908.)
 
(Read before the Anatomical Society of Great Britain and Ireland, at Birniingham, 26th June 1908.)
  
A LITTLE time ago my colleague, Dr Arthur Hall, kindly handed me over
+
A little time ago my colleague, Dr Arthur Hall, kindly handed me over for the Anatomical Museum, among other specimens. a human embryo 5 mm. in length. No history as to how the specimen was obtained can be traced, but apparently it was expelled from the uterus as a “ miscarriage," the membranes and decidua; being intact. A11 oval - shaped tumour (length 2'5 em., breadth 1'5 cm.), hard and dense, which on section proved to be a blood-clot, was found attached to one end of the mass (fig. 1, 1'). From inquiries made, it would seem that the specimen had lain in spirit for many years in the Pathological Museum of the old University College. It was suspended in a glass jar by means of a wire passed through the blood~ clot and attached to the lid. Except that neither the clot nor the amnion had been c11t into, the specimen, when I received it, appeared as in fig. 1, which is a reproduction of a photograph of natural dimensions. The abnormal position of the amnion, dislodged from the chorionic vesicle, and hanging as a pear—shaped bag, attracted attention, but its immense size struck one as 1nucl1 more peculiar. The maximum length and breadth of the unopened sac measured respectively 32 c111. and 2'2 cm., which were altogether disproportionate to the size of the minute embryo contained within. In fact, when replaced the amnion not only filled but pressed upon the cavity of tlie chorion, though normally the obliteration of the extra- embryonic c<elom does not take place before the embryo is eight weeks old and would measure about 30 mm. The body—stalk was relatively short, so that the embryo occupied the upper part of the sac (fig. 1,j), contrasted with the position which the long stalk of an embryo of later date permits. The amnion in question had evidently undergone abnormal distension. lt was filled with a light yellowish—red fluid which took from its translucency, obscuring the embryo to such an extent that the latter appeared little more than a minute dark shadow within. Fearing that I had lost my bearings and that the supposed amnion was perhaps some part of the chorionic investment split off1 and that a closely investing membrane was yet to be
for the Anatomical Museum, among other specimens. a human embryo
 
5 mm. in length. No history as to how the specimen was obtained can be
 
traced, but apparently it was expelled from the uterus as a “ miscarriage,"
 
the membranes and decidua; being intact. A11 oval - shaped tumour
 
(length 2'5 em., breadth 1'5 cm.), hard and dense, which on section proved
 
to be a blood-clot, was found attached to one end of the mass (fig. 1, 1').
 
From inquiries made, it would seem that the specimen had lain in spirit for
 
many years in the Pathological Museum of the old University College. It
 
was suspended in a glass jar by means of a wire passed through the blood~
 
clot and attached to the lid. Except that neither the clot nor the amnion
 
had been c11t into, the specimen, when I received it, appeared as in fig. 1,
 
which is a reproduction of a photograph of natural dimensions. The
 
abnormal position of the amnion, dislodged from the chorionic vesicle, and
 
hanging as a pear—shaped bag, attracted attention, but its immense size
 
struck one as 1nucl1 more peculiar. The maximum length and breadth of
 
the unopened sac measured respectively 32 c111. and 2'2 cm., which were
 
altogether disproportionate to the size of the minute embryo contained
 
within. In fact, when replaced the amnion not only filled but pressed upon
 
the cavity of tlie chorion, though normally the obliteration of the extra-
 
embryonic c<elom does not take place before the embryo is eight weeks old and
 
would measure about 30 mm. The body—stalk was relatively short, so that
 
the embryo occupied the upper part of the sac (fig. 1,j), contrasted with the
 
position which the long stalk of an embryo of later date permits. The
 
amnion in question had evidently undergone abnormal distension. lt was
 
filled with a light yellowish—red fluid which took from its translucency,
 
obscuring the embryo to such an extent that the latter appeared little more
 
than a minute dark shadow within. Fearing that I had lost my bearings
 
and that the supposed amnion was perhaps some part of the chorionic
 
investment split off1 and that a closely investing membrane was yet to be
 
  
1 I may here state that, i11 addition to the thick trophoblastic layer of the choriou
 
profusely beset with villi, the mesodermic layer was present in the form of :1 thin and very
 
236 Mr C. J. Patten
 
  
discovered, I proceeded with as much caution as possible to explore the
+
* 1 I may here state that, in addition to the thick trophoblastic layer of the choriou profusely beset with villi, the mesodermic layer was present in the form of :1 thin and very
interior of the sac by cutting a window in it over the area where the
+
discovered, I proceeded with as much caution as possible to explore the interior of the sac by cutting a window in it over the area where the embryo was suspended (fig. 1, a,,f). The first slight snip made with a finely pointed pair of scissors demonstrated the distensibility of the sac by
embryo was suspended (fig. 1, a,,f). The first slight snip made with a
 
finely pointed pair of scissors demonstrated the distensibility of the sac by
 
  
FIG. l.—The embryo in situ and its surrounding tissues. (Nat. size.) The specimen
+
FIG. 1.—The embryo in situ and its surrounding tissues. (Nat. size.) The specimen was photographed under spirit after the amnion had been opened and the turbid liquor amnii removed by gentle irrigation through a finely pointed pipette.
was photographed under spirit after the amnion had been opened and the turbid
 
liquor amnii removed by gentle irrigation through a finely pointed pipette.
 
  
The enlarged amniotic sac (a), dlsplaced from the chorionlc vesicle (b), hangs downwards. A window
+
The enlarged amniotic sac (a), dlsplaced from the chorionlc vesicle (b), hangs downwards. A window has been cut into the sac to allow the contained embryo (f) to come into view. The chorionic villi (c) are seen connected with the decldua (d). The oval-shaped blood-clot (e) is attached at the upper end of the decldua.
has been cut into the sac to allow the contained embryo (f) to come into view. The chorionic
 
villi (c) are seen connected with the decldua (d). The oval-shaped blood-clot (e) is attached at
 
the upper end of the decldua.
 
  
 
N.B.—Thls photograph being natural size, it may be of interest to give the following measurements :—
 
N.B.—Thls photograph being natural size, it may be of interest to give the following measurements :—
  
Total length (mm top of clot to tip of amnion. 91 cm.
+
Total length (mm top of clot to tip of amnion. 9.1 cm. Greatest length of amnion 32 cm.; greatest breadth, 2.2 cm. Longest measurement of clot, 2.5 cm. ; broadest, 1.5 cm. Greatest length of chorlonic cavity, 3.4 cm.
Greatest length of amnion 32 cm.; greatest breadth, 2'2 cm.
 
Longest measurement of clot, 2'5 cm. ; broadest, 1*5 cm.
 
Greatest length of chorlonic cavity, 3'4 cm.
 
  
the rush of semi-turbid fluid Which, when cleared away by gentle irriga-
+
the rush of semi-turbid fluid Which, when cleared away by gentle irriga- tion with clean spirit through a fine pipette, left the amniotic wall as clear delicate membrane loosely adherent to the trophoblastic layer, and from which it  easily separated. A prion’ therefore, the supposed ammon could not have been the inner layer of the chorion. Indeed, as the text shows, it proved to be the true amniotic covering.
tion with clean spirit through a fine pipette, left the amniotic wall as clear
 
  
delicate membrane loosely adherent to the trophoblastic layer, and from which it ‘easily
+
as usual. The opacity, therefore, was not due to thickenings of the wall, but to the turbidity of the contained fluid. I next looked carefully for a closely investing membrane, but found the embryo free from such. Distension of the amnion by an unusually large quantity of liquor amnii, associated with an embryo of so early a stage of development, appears to be a very rare condition. I do not pretend to offer a satisfactory explanation, but may say in passing that I have found somewhat parallel instances among avian embryos which had been killed by raising the temperature of an incubator to 46" C. and over. In three species — House-sparrow, Song- thrush, and Blackbird — the amnion was hyper-distended with fluid. In- deed, it may be suggested that the inflammatory conditions which induced the haemorrhage may have been accompanied by a rise in temperature suflicient to kill the human embryo in question and, moreover, to call forth an exudation of liquor amnii with excessive distension of the sac; for, shall be pointed out presently, the embryo bore evident signs that it had been dead some time before it was expelled from the uterus.
  
separated. A prion’ therefore, the supposed ammon could not have been the inner layer of
 
the chorion. Indeed, as the text shows, it proved to be the true amniotic covering.
 
External Features of Early Human Embryo with Distended Amnion 237
 
  
as usual. The opacity, therefore, was not due to thickenings of the wall,
+
I next photographed the embryo in situ, and then proceeded to free it from its connection with the amnion. I11 this attempt a portion of the pear-shaped yolk-sac came away. It communicated by a wide neck with the alimentary canal, and was about two-thirds the length (in its longest dimension) of the body of the embryo. In fig. 2 the parts which are intact, I) and r, together with the area enclosed within the dotted line, indicate the shape and the size relative to the embryo. The distal end of the short body-stalk, where it was disconnected from the amnion, was expanded and disc-like (fig. 2, (L). Both it and the yolk-sac were exceedingly thin and frail. The embryo, while retaining its natural shape, was soft and cheese- like in consistency, and so fragile as to allow of little manipulation even with a soft camel-hair brush. It evidently died in utaro and remained for seine days soaking in the liquor amnii. A There is no evidence to show that the deterioration of the tissues was due to neglect in preserving the specimen after it had been secured; for the clot, deciduee, chorionic villi, and membranes are well preserved, having probably retained their vitality for a considerable time after the death of the embryo.
but to the turbidity of the contained fluid. I next looked carefully for a
 
closely investing membrane, but found the embryo free from such. Distension
 
of the amnion by an unusually large quantity of liquor amnii, associated
 
with an embryo of so early a stage of development, appears to be a very
 
rare condition. I do not pretend to offer a satisfactory explanation, but
 
may say in passing that I have found somewhat parallel instances among
 
avian embryos which had been killed by raising the temperature of an
 
incubator to 46" C. and over. In three species—House-sparrow, Song-
 
thrush, and Blackbird—the amnion was hyper-distended with fluid. In-
 
deed, it may be suggested that the inflammatory conditions which induced
 
the haemorrhage may have been accompanied by a rise in temperature
 
suflicient to kill the human embryo in question and, moreover, to call forth
 
an exudation of liquor amnii with excessive distension of the sac; for,
 
shall be pointed out presently, the embryo bore evident signs that it had
 
been dead some time before it was expelled from the uterus.
 
  
I next photographed the embryo in situ, and then proceeded to free it
+
Examined in spirit, the embryo was of a greyish-wlnte colour and very opaque. The mouth, bounded above by the prominent fore-brain and below by a well-developed mandibular arch and prominent heart, the optic Vesicle, the four limb-buds (just appearing as slight prominences), the downwardly directed tail, and a rather sharp dorsiflexion opposite the arm-buds were about the only features that could be made out.
from its connection with the amnion. I11 this attempt a portion of the
 
pear-shaped yolk-sac came away. It communicated by a wide neck with
 
the alimentary canal, and was about two-thirds the length (in its longest
 
dimension) of the body of the embryo. In fig. 2 the parts which are intact,
 
I) and r, together with the area enclosed within the dotted line, indicate the
 
shape and the size relative to the embryo. The distal end of the short
 
body-stalk, where it was disconnected from the amnion, was expanded and
 
disc-like (fig. 2, (L). Both it and the yolk-sac were exceedingly thin and
 
frail. The embryo, while retaining its natural shape, was soft and cheese-
 
like in consistency, and so fragile as to allow of little manipulation
 
even with a soft camel-hair brush. It evidently died in utaro and remained
 
for seine days soaking in the liquor amnii. A There is no evidence to show
 
that the deterioration of the tissues was due to neglect in preserving the
 
specimen after it had been secured; for the clot, deciduee, chorionic villi,
 
and membranes are well preserved, having probably retained their vitality
 
for a considerable time after the death of the embryo.
 
  
Examined in spirit, the embryo was of a greyish-wlnte colour and very
+
On passing the specimen through a series of diluted baths until pure water was reached, several other details became apparent. Examined under water after two hours’ soaking, the embryo showed a well-marked, pit-like, depression immediately below the mandibular arch. Microscopic examina- tion with careful focussing further revealed a delicate linear shading extending backward and upward. The whole I take to be the hyo-mandibular cleft; this is bounded below by a short and less distinctly marked ridge-the hyoidean arch. Ventrally, this arch appears to join the mandibular arch. Another pit-like depression, extending a short distance backward as a faint linear shading and presumably the second branchial cleft, appears below the hyoidean arch.  
opaque. The mouth, bounded above by the prominent fore-brain and below
 
by a well-developed mandibular arch and prominent heart, the optic Vesicle,
 
the four limb-buds (just appearing as slight prominences), the downwardly
 
directed tail, and a rather sharp dorsiflexion opposite the arm-buds were
 
about the only features that could be made out.
 
  
On passing the specimen through a series of diluted baths until pure
+
Fig. 2.—Embryo from the left side. The photopraph was taken as the embryo lay in water in which it had previous y soaked for two hours, having been removed from spirituous solutions.
water was reached, several other details became apparent. Examined under
 
238 Mr C. J. Patten
 
  
water after two hours’ soaking, the embryo showed a well-marked, pit—1ike,
+
Below the heart and separated by a tag of membrane is the right arm-bud, shaped like a minute bi-convex lens. The left arm-bud is also visible as a slight and somewhat shaded prominence opposite the sharpest bend of the back. below which several mesoblastic somites are faintly discernible. The left leg-bud, flssured transversely, appears as a distinct oval-shaped elevation a little way above the point of the tail. Opposite the leg-bud a gentle convexity of the dorsal surface indicates the position of the commencing sacral bend. The lower end of the body-stalk (a) appears as in wide flattened disc on which the tail-end of the embryo rests. The portions of the yolk-sac which remained intactare lettered b and c. The dark area enclosed within the dotted line represents what was torn away. The other features of the embryo can be made out from the description in the text, and a reference to flg.3 (lettered).
depression immediately below the mandibular arch. Microscopic examina-
 
tion with careful focussing further revealed a delicate linear shading
 
extending backward and upward. The whole I take to be the hyo—
 
mandibular cleft; this is bounded below by a short and less distinctly
 
  
Fig. 2.—Embryo from the left side. The photopraph was taken as the
 
embryo lay in water in which it had previous y soaked for two hours,
 
having been removed from spirituous solutions.
 
  
Below the heart and separated by a tag of membrane is the right arm-bud, shaped like a
 
minute bi-convex lens. The left arm-bud is also visible as a slight and somewhat
 
shaded prominence opposite the sharpest bend of the back. below which several
 
mesoblastic somites are faintly discernible. The left leg-bud, flssured transversely,
 
appears as a distinct oval-shaped elevation a little way above the point of the tail.
 
Opposite the leg-bud a gentle convexity of the dorsal surface indicates the position
 
of the commencing sacral bend. The lower end of the body-stalk (a) appears as in
 
wide flattened disc on which the tail-end of the embryo rests. The portions of the
 
yolk-sac which remained intactare lettered b and c. The dark area enclosed within
 
the dotted line represents what was torn away. The other features of the embryo
 
can be made out from the description in the text, and a reference to flg.3(lettered).
 
  
marked ridge—the hyoidean arch. Ventrally, this arch appears to join the
+
Fig. 3. Drawing of the embryo from the left side. The drawing was made when the embryo was under water and had been soaking two hours after the photograph (fig. 2) was taken.
mandibular arch. Another pit-like depression, extending a short distance
 
  
backward as a faint linear shading and presumably the second branchial
+
a, mnndibular arch; b, hyoidean arch. Between a and b is seen the hyo-mandibular cleft, re resented by a deep pit ventrally and a. thin linear shading when followed backward. Below b is t e second branohial cleft, also seen as I distinct pit-like depression in from, but shading ofl indistinctly when traced backward; a, heart; 6', pericardium, showing torn ends; 11, right arm-bud; 41’, left arm-bud; e, mesoblastic somltes, very indistinct; , lett leg-bud; . tall, downwardly directed; h, remnins of sllantois; i, neck of yolk-soc. whose t in walls have co lspsed and closed the cavity. 240 Mr C. J. Patten
cleft, appears below the hyoidean arch.
 
External Features‘ of Early Human Embryo with Distended Amnion 239
 
  
Fig. 3.—Dra.wing of the embryo from the left side. The drawing was made
+
Though I allowed the embryo to remain some hours longer in water, until the parts visible in spirit became much more clearly defined, and indications of mesoblastic somites could be faintly discerned below the dorsiflexions (figs. 2 and 3), I am satisfied that no other traces of gill- slits could be found. Comparing this embryo With" others, it may be seen that the downwardly directed tail, sharp back curve (dorsifiexion), large wide—necked yolk—sac, wide body—stalk, prominent bent tubular heart, and the presence of only two gill—slits‘ would point to characteristics of an embryo of smaller size and earlier date. Such, for instance, are, for the most part, to be made out in His’s Lg embryo, which is only 2'15 mm. long, though here the dorsiflexion is more pronounced. While often accompany- ing embryos of between 2 and 3 mm. long, still the dorsiflexion varies considerably in extent: for instance, in Kollmann’s embryo, 2‘4.« mm., the dorsal surface of the body, though not sharply bent like that of His’s Lg embryo, is distinctly concave from before backward, while Professor Peter Thompson’s2 specimen of the same dimensions shows no dorsiflexion, the whole back being evenly convex, and the head a11d tail curved toward each other. V
when the embryo was under water and had been soaking two hours
 
after the photograph (fig. 2) was taken.
 
  
a, mnndibular arch; b, hyoidean arch. Between a and b is seen the hyo-mandibular cleft, re resented
+
On the other hand, the fuller and more rounded head, conspicuous eye- vesicle, and mandibular arch, with the first indications of the limb-buds, recall the features of His’s Lr embryo of 42 mm. long, estimated at about three weeks old. The main difference is that in the latter the dorsiflexion has almost entirely disappeared and has been‘ replaced by a distinct ventral bending of both the anterior and posterior parts with marked convexities over the head and neck and sacral regions, the tail being distinctly curled upward. In this embryo a third branchial cleft is figured as well as a distinct otic vesicle.
by a deep pit ventrally and a. thin linear shading when followed backward. Below b is t e second
 
branohial cleft, also seen as I distinct pit-like depression in from, but shading ofl indistinctly
 
when traced backward; a, heart; 6', pericardium, showing torn ends; 11, right arm-bud; 41’, left
 
arm-bud; e, mesoblastic somltes, very indistinct; , lett leg-bud; . tall, downwardly directed;
 
h, remnins of sllantois; i, neck of yolk-soc. whose t in walls have co lspsed and closed the cavity.
 
240 Mr C. J. Patten
 
  
Though I allowed the embryo to remain some hours longer in water,
+
With regard to the chorion there is little to add beyond noting that it was well developed, and villi covered its entire surface, being specially well marked and thick at the region most remote from the blood-clot (fig. 1). The average length of the villous tufts, measured from their roots on the outer surface of the trophoblastic chorion to their attachments in the deciduae, was about 8 cm. Taken as a whole, the villi varied from thick, irregular, lobed processes to slender, dendritic arborisations. The delicate inner chorionic mesoderm could be separated without difliculty from the stout outer trophoblastic layer.
until the parts visible in spirit became much more clearly defined, and
 
indications of mesoblastic somites could be faintly discerned below the
 
dorsiflexions (figs. 2 and 3), I am satisfied that no other traces of gill-
 
slits could be found. Comparing this embryo With" others, it may be seen
 
that the downwardly directed tail, sharp back curve (dorsifiexion), large
 
wide—necked yolk—sac, wide body—stalk, prominent bent tubular heart, and
 
the presence of only two gill—slits‘ would point to characteristics of an
 
embryo of smaller size and earlier date. Such, for instance, are, for the
 
most part, to be made out in His’s Lg embryo, which is only 2'15 mm. long,
 
though here the dorsiflexion is more pronounced. While often accompany-
 
ing embryos of between 2 and 3 mm. long, still the dorsiflexion varies
 
considerably in extent: for instance, in Kollmann’s embryo, 2‘4.« mm., the
 
dorsal surface of the body, though not sharply bent like that of His’s Lg
 
embryo, is distinctly concave from before backward, while Professor Peter
 
Thompson’s2 specimen of the same dimensions shows no dorsiflexion, the
 
whole back being evenly convex, and the head a11d tail curved toward
 
each other. V
 
  
On the other hand, the fuller and more rounded head, conspicuous eye-
+
* 1 Unless the other two gill-slits had already closed up. 2 In this specimen the head is “small, somewhat flattened from above downward and pointed,” differing considerably from the form of head in most young human embryos. External Features of Early Human Embryo with Distended Amnion 241
vesicle, and mandibular arch, with the first indications of the limb-buds,
 
recall the features of His’s Lr embryo of 42 mm. long, estimated at about
 
three weeks old. The main difference is that in the latter the dorsiflexion
 
has almost entirely disappeared and has been‘ replaced by a distinct ventral
 
bending of both the anterior and posterior parts with marked convexities
 
over the head and neck and sacral regions, the tail being distinctly curled
 
upward. In this embryo a third branchial cleft is figured as well as a
 
distinct otic vesicle.
 
  
With regard to the chorion there is little to add beyond noting that it
+
==Summary==
was well developed, and villi covered its entire surface, being specially well
 
marked and thick at the region most remote from the blood-clot (fig. 1).
 
The average length of the villous tufts, measured from their roots on the
 
outer surface of the trophoblastic chorion to their attachments in the
 
deciduae, was about 8 cm. Taken as a whole, the villi varied from thick,
 
irregular, lobed processes to slender, dendritic arborisations. The delicate
 
inner chorionic mesoderm could be separated without difliculty from the
 
  
stout outer trophoblastic layer.
+
Useless as the embryo above described may be for cutting and mounting, it lacks nothing in the perfection of its external form; indeed, the word “pathological,” often too loosely applied in embryology, would here be quite inapplicable. This, coupled with the fact that early human embryos are diflicult to procure, leads me to believe that, handicapped though I have been in my attempts to describe and figure so frail a specimen, such will not be devoid of interest. An examination of the external features alone of this specimen affords us another striking instance of the wide range of variation to be met with in embryos of somewhat the same size and supposed age. If adherence to type be strictly enforced, the embryo here described is decidedly aberrant. Some of its features point to precocity of development; others to tardiness.
  
1 Unless the other two gill-slits had already closed up.
+
When one considers not only the remarkable diflerences noticeable in the early post-natal development of large clutches of birds and litters of mammals, "but also in the pre-natal growth of several embryos within the same uterus, and, less frequently, though by no means rarely, of twins, it would seem almost surprising than otherwise if human embryos of similar period, but from difierent uteri, should reach with any degree of constancy the same state of development and exhibit the same external features.
2 In this specimen the head is “small, somewhat flattened from above downward and
 
  
pointed,” differing considerably from the form of head in most young human embryos.
+
In conclusion, I wish to express my indebtedness to Dr W. J. Vincent for the drawing he so kindly made, from which fig. 3 has been prepared.
External Features of Early Human Embryo with Distended Amnion 241
 
 
 
SUMMARY.
 
 
 
Useless as the embryo above described may be for cutting and mounting,
 
it lacks nothing in the perfection of its external form; indeed, the word
 
“pathological,” often too loosely applied in embryology, would here be
 
quite inapplicable. This, coupled with the fact that early human embryos
 
are diflicult to procure, leads me to believe that, handicapped though I
 
have been in my attempts to describe and figure so frail a specimen, such
 
will not be devoid of interest. An examination of the external features
 
alone of this specimen affords us another striking instance of the wide range
 
of variation to be met with in embryos of somewhat the same size and
 
supposed age. If adherence to type be strictly enforced, the embryo here
 
described is decidedly aberrant. Some of its features point to precocity of
 
development; others to tardiness.
 
 
 
When one considers not only the remarkable diflerences noticeable in
 
the early post-natal development of large clutches of birds and litters of
 
mammals, "but also in the pre-natal growth of several embryos within the
 
same uterus, and, less frequently, though by no means rarely, of twins, it
 
would seem almost surprising than otherwise if human embryos of similar
 
period, but from difierent uteri, should reach with any degree of constancy
 
the same state of development and exhibit the same external features.
 
 
 
In conclusion, I wish to express my indebtedness to Dr W. J. Vincent
 
for the drawing he so kindly made, from which fig. 3 has been prepared.
 
  
 
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Patten CJ. External Features of an Early Human Embryo with a Distended Amnion. (1909) J Anat Physiol. 43(3): 235-241. PMID: 17232803

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This 1909 paper by Patten is an early investigation of abnormal development in human embryos.



Modern Notes:

Abnormality Links: abnormal development | abnormal genetic | abnormal environmental | Unknown | teratogens | ectopic pregnancy | cardiovascular abnormalities | coelom abnormalities | endocrine abnormalities | gastrointestinal abnormalities | genital abnormalities | head abnormalities | integumentary abnormalities | musculoskeletal abnormalities | limb abnormalities | neural abnormalities | neural crest abnormalities | placenta abnormalities | renal abnormalities | respiratory abnormalities | hearing abnormalities | vision abnormalities | twinning | Developmental Origins of Health and Disease |  ICD-11
Historic Embryology  
1915 Congenital Cardiac Disease | 1917 Frequency of Anomalies in Human Embryos | 1920 Hydatiform Degeneration Tubal Pregnancy | 1921 Anencephalic Embryo | 1921 Rat and Man | 1966 Congenital Malformations
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External Features of an Early Human Embryo with a Distended Amnion

By C. J. PATTEN, Sc.

(Read before the Anatomical Society of Great Britain and Ireland, at Birniingham, 26th June 1908.)

A little time ago my colleague, Dr Arthur Hall, kindly handed me over for the Anatomical Museum, among other specimens. a human embryo 5 mm. in length. No history as to how the specimen was obtained can be traced, but apparently it was expelled from the uterus as a “ miscarriage," the membranes and decidua; being intact. A11 oval - shaped tumour (length 2'5 em., breadth 1'5 cm.), hard and dense, which on section proved to be a blood-clot, was found attached to one end of the mass (fig. 1, 1'). From inquiries made, it would seem that the specimen had lain in spirit for many years in the Pathological Museum of the old University College. It was suspended in a glass jar by means of a wire passed through the blood~ clot and attached to the lid. Except that neither the clot nor the amnion had been c11t into, the specimen, when I received it, appeared as in fig. 1, which is a reproduction of a photograph of natural dimensions. The abnormal position of the amnion, dislodged from the chorionic vesicle, and hanging as a pear—shaped bag, attracted attention, but its immense size struck one as 1nucl1 more peculiar. The maximum length and breadth of the unopened sac measured respectively 32 c111. and 2'2 cm., which were altogether disproportionate to the size of the minute embryo contained within. In fact, when replaced the amnion not only filled but pressed upon the cavity of tlie chorion, though normally the obliteration of the extra- embryonic c<elom does not take place before the embryo is eight weeks old and would measure about 30 mm. The body—stalk was relatively short, so that the embryo occupied the upper part of the sac (fig. 1,j), contrasted with the position which the long stalk of an embryo of later date permits. The amnion in question had evidently undergone abnormal distension. lt was filled with a light yellowish—red fluid which took from its translucency, obscuring the embryo to such an extent that the latter appeared little more than a minute dark shadow within. Fearing that I had lost my bearings and that the supposed amnion was perhaps some part of the chorionic investment split off1 and that a closely investing membrane was yet to be


  • 1 I may here state that, in addition to the thick trophoblastic layer of the choriou profusely beset with villi, the mesodermic layer was present in the form of :1 thin and very

discovered, I proceeded with as much caution as possible to explore the interior of the sac by cutting a window in it over the area where the embryo was suspended (fig. 1, a,,f). The first slight snip made with a finely pointed pair of scissors demonstrated the distensibility of the sac by

FIG. 1.—The embryo in situ and its surrounding tissues. (Nat. size.) The specimen was photographed under spirit after the amnion had been opened and the turbid liquor amnii removed by gentle irrigation through a finely pointed pipette.

The enlarged amniotic sac (a), dlsplaced from the chorionlc vesicle (b), hangs downwards. A window has been cut into the sac to allow the contained embryo (f) to come into view. The chorionic villi (c) are seen connected with the decldua (d). The oval-shaped blood-clot (e) is attached at the upper end of the decldua.

N.B.—Thls photograph being natural size, it may be of interest to give the following measurements :—

Total length (mm top of clot to tip of amnion. 9.1 cm. Greatest length of amnion 32 cm.; greatest breadth, 2.2 cm. Longest measurement of clot, 2.5 cm. ; broadest, 1.5 cm. Greatest length of chorlonic cavity, 3.4 cm.

the rush of semi-turbid fluid Which, when cleared away by gentle irriga- tion with clean spirit through a fine pipette, left the amniotic wall as clear delicate membrane loosely adherent to the trophoblastic layer, and from which it easily separated. A prion’ therefore, the supposed ammon could not have been the inner layer of the chorion. Indeed, as the text shows, it proved to be the true amniotic covering.

as usual. The opacity, therefore, was not due to thickenings of the wall, but to the turbidity of the contained fluid. I next looked carefully for a closely investing membrane, but found the embryo free from such. Distension of the amnion by an unusually large quantity of liquor amnii, associated with an embryo of so early a stage of development, appears to be a very rare condition. I do not pretend to offer a satisfactory explanation, but may say in passing that I have found somewhat parallel instances among avian embryos which had been killed by raising the temperature of an incubator to 46" C. and over. In three species — House-sparrow, Song- thrush, and Blackbird — the amnion was hyper-distended with fluid. In- deed, it may be suggested that the inflammatory conditions which induced the haemorrhage may have been accompanied by a rise in temperature suflicient to kill the human embryo in question and, moreover, to call forth an exudation of liquor amnii with excessive distension of the sac; for, shall be pointed out presently, the embryo bore evident signs that it had been dead some time before it was expelled from the uterus.


I next photographed the embryo in situ, and then proceeded to free it from its connection with the amnion. I11 this attempt a portion of the pear-shaped yolk-sac came away. It communicated by a wide neck with the alimentary canal, and was about two-thirds the length (in its longest dimension) of the body of the embryo. In fig. 2 the parts which are intact, I) and r, together with the area enclosed within the dotted line, indicate the shape and the size relative to the embryo. The distal end of the short body-stalk, where it was disconnected from the amnion, was expanded and disc-like (fig. 2, (L). Both it and the yolk-sac were exceedingly thin and frail. The embryo, while retaining its natural shape, was soft and cheese- like in consistency, and so fragile as to allow of little manipulation even with a soft camel-hair brush. It evidently died in utaro and remained for seine days soaking in the liquor amnii. A There is no evidence to show that the deterioration of the tissues was due to neglect in preserving the specimen after it had been secured; for the clot, deciduee, chorionic villi, and membranes are well preserved, having probably retained their vitality for a considerable time after the death of the embryo.

Examined in spirit, the embryo was of a greyish-wlnte colour and very opaque. The mouth, bounded above by the prominent fore-brain and below by a well-developed mandibular arch and prominent heart, the optic Vesicle, the four limb-buds (just appearing as slight prominences), the downwardly directed tail, and a rather sharp dorsiflexion opposite the arm-buds were about the only features that could be made out.

On passing the specimen through a series of diluted baths until pure water was reached, several other details became apparent. Examined under water after two hours’ soaking, the embryo showed a well-marked, pit-like, depression immediately below the mandibular arch. Microscopic examina- tion with careful focussing further revealed a delicate linear shading extending backward and upward. The whole I take to be the hyo-mandibular cleft; this is bounded below by a short and less distinctly marked ridge-the hyoidean arch. Ventrally, this arch appears to join the mandibular arch. Another pit-like depression, extending a short distance backward as a faint linear shading and presumably the second branchial cleft, appears below the hyoidean arch.

Fig. 2.—Embryo from the left side. The photopraph was taken as the embryo lay in water in which it had previous y soaked for two hours, having been removed from spirituous solutions.

Below the heart and separated by a tag of membrane is the right arm-bud, shaped like a minute bi-convex lens. The left arm-bud is also visible as a slight and somewhat shaded prominence opposite the sharpest bend of the back. below which several mesoblastic somites are faintly discernible. The left leg-bud, flssured transversely, appears as a distinct oval-shaped elevation a little way above the point of the tail. Opposite the leg-bud a gentle convexity of the dorsal surface indicates the position of the commencing sacral bend. The lower end of the body-stalk (a) appears as in wide flattened disc on which the tail-end of the embryo rests. The portions of the yolk-sac which remained intactare lettered b and c. The dark area enclosed within the dotted line represents what was torn away. The other features of the embryo can be made out from the description in the text, and a reference to flg.3 (lettered).


Fig. 3. Drawing of the embryo from the left side. The drawing was made when the embryo was under water and had been soaking two hours after the photograph (fig. 2) was taken.

a, mnndibular arch; b, hyoidean arch. Between a and b is seen the hyo-mandibular cleft, re resented by a deep pit ventrally and a. thin linear shading when followed backward. Below b is t e second branohial cleft, also seen as I distinct pit-like depression in from, but shading ofl indistinctly when traced backward; a, heart; 6', pericardium, showing torn ends; 11, right arm-bud; 41’, left arm-bud; e, mesoblastic somltes, very indistinct; , lett leg-bud; . tall, downwardly directed; h, remnins of sllantois; i, neck of yolk-soc. whose t in walls have co lspsed and closed the cavity. 240 Mr C. J. Patten

Though I allowed the embryo to remain some hours longer in water, until the parts visible in spirit became much more clearly defined, and indications of mesoblastic somites could be faintly discerned below the dorsiflexions (figs. 2 and 3), I am satisfied that no other traces of gill- slits could be found. Comparing this embryo With" others, it may be seen that the downwardly directed tail, sharp back curve (dorsifiexion), large wide—necked yolk—sac, wide body—stalk, prominent bent tubular heart, and the presence of only two gill—slits‘ would point to characteristics of an embryo of smaller size and earlier date. Such, for instance, are, for the most part, to be made out in His’s Lg embryo, which is only 2'15 mm. long, though here the dorsiflexion is more pronounced. While often accompany- ing embryos of between 2 and 3 mm. long, still the dorsiflexion varies considerably in extent: for instance, in Kollmann’s embryo, 2‘4.« mm., the dorsal surface of the body, though not sharply bent like that of His’s Lg embryo, is distinctly concave from before backward, while Professor Peter Thompson’s2 specimen of the same dimensions shows no dorsiflexion, the whole back being evenly convex, and the head a11d tail curved toward each other. V

On the other hand, the fuller and more rounded head, conspicuous eye- vesicle, and mandibular arch, with the first indications of the limb-buds, recall the features of His’s Lr embryo of 42 mm. long, estimated at about three weeks old. The main difference is that in the latter the dorsiflexion has almost entirely disappeared and has been‘ replaced by a distinct ventral bending of both the anterior and posterior parts with marked convexities over the head and neck and sacral regions, the tail being distinctly curled upward. In this embryo a third branchial cleft is figured as well as a distinct otic vesicle.

With regard to the chorion there is little to add beyond noting that it was well developed, and villi covered its entire surface, being specially well marked and thick at the region most remote from the blood-clot (fig. 1). The average length of the villous tufts, measured from their roots on the outer surface of the trophoblastic chorion to their attachments in the deciduae, was about 8 cm. Taken as a whole, the villi varied from thick, irregular, lobed processes to slender, dendritic arborisations. The delicate inner chorionic mesoderm could be separated without difliculty from the stout outer trophoblastic layer.

  • 1 Unless the other two gill-slits had already closed up. 2 In this specimen the head is “small, somewhat flattened from above downward and pointed,” differing considerably from the form of head in most young human embryos. External Features of Early Human Embryo with Distended Amnion 241

Summary

Useless as the embryo above described may be for cutting and mounting, it lacks nothing in the perfection of its external form; indeed, the word “pathological,” often too loosely applied in embryology, would here be quite inapplicable. This, coupled with the fact that early human embryos are diflicult to procure, leads me to believe that, handicapped though I have been in my attempts to describe and figure so frail a specimen, such will not be devoid of interest. An examination of the external features alone of this specimen affords us another striking instance of the wide range of variation to be met with in embryos of somewhat the same size and supposed age. If adherence to type be strictly enforced, the embryo here described is decidedly aberrant. Some of its features point to precocity of development; others to tardiness.

When one considers not only the remarkable diflerences noticeable in the early post-natal development of large clutches of birds and litters of mammals, "but also in the pre-natal growth of several embryos within the same uterus, and, less frequently, though by no means rarely, of twins, it would seem almost surprising than otherwise if human embryos of similar period, but from difierent uteri, should reach with any degree of constancy the same state of development and exhibit the same external features.

In conclusion, I wish to express my indebtedness to Dr W. J. Vincent for the drawing he so kindly made, from which fig. 3 has been prepared.


Cite this page: Hill, M.A. (2020, April 5) Embryology Paper - External features of an early human embryo with a distended amnion. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_External_features_of_an_early_human_embryo_with_a_distended_amnion

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