Book - Uterine and tubal gestation (1903) 1-7
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Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
|zygote, morula, and blastocyst stages with implantation occurring in week 2.|
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Part I. The Essentials of Uterine Gestation
Chapter VII. The Further Development of the Human Ovum
The Early Development of the Embryonal Area
1. The ovum v. H., described by Spee, was thrown off after five weeks menopause. The ovum contains an oval germinal plate entirely in the stage of the primitive streak and situated in the wall of the amniotic cavity. The entire embryonal formation is 0.4 millimetre long. The greatest diameter of the ovum including the villi is 5% to 7 millimetres. Under the chorion was found a thin layer of connective tissue poor in cells and bounding directly the mesodermal slit. From this layer the chorion could be lifted off. The inner part of the ovum contained a bubble of air and a non-celled fibred coagulation substance in which, on the serotinal side, was seen the embryonal formation, which included the amniotic cavity with the germinal plate and the umbilical vesicle (Fig. 25).
Fig. 25. — Ovum v.H. (Spee), showing embryonal and extra-embryonal areas. The extra-embryonal villi and membrana chorii are connected with the embryonal formation by the adherent band of mesoderm.
The primitive streak region is small, and yet the development of mesoderm within the chorion, in the abdominal pedicle and about the amniotic cavity and about the umbilical vesicle, is so great that considerable time must have been needed for its development. At the time when the mesoderm began to develop, the ovum was probably of a diameter of 0.5 millimetre. At the first beginning of the mesoderm slit the ovum was probably of a diameter of 1 millimetre.
The embryonal formation is a long, thick projection connected at one end with the inner side of the chorion, but otherwise projecting free into the cavity of the vesicle, that is, the periembryonal mesoderm slit (Fig. 25). A superficial transverse furrow divides it into two elliptical parts. The larger is at the free end and contains the entoderm vesicle. The smaller part contains the amniotic cavity lined with ectoderm and consists, in addition, of the compact band of mesoderm which covers threefourths of the amnion, from the mesodermal covering of the entoderm vesicle up to the chorion (Fig. 26) . This compact band is the adherent pedicle and corresponds to the caudal end of the primitive streak. The entoderm vesicle sends a blind duct, lined with entoderm, into the adherent pedicle. The entoderm vesicle lined with a single row of cubical cells, and covered with mesoderm, is the umbilical vesicle. The amniotic cavity is lined with ectoderm and is likewise covered with mesoderm. The single layer of flat cells lining the amniotic cavity begins to thicken at a certain point ; the cells become high cylindrical and constitute the germinal plate. That part of the ectoderm of the amniotic cavity lying on the umbilical vesicle enters, then, into the formation of this thick germinal plate. The mesoderm which covers the umbilical vesicle and the amnion unites in the narrow zone which separates the two. Here where the walls of the umbilical vesicle and amnion run parallel, the germinal plate is found on the inner surface of the amniotic cavity. From the caudal knot up to the chorion extends the adherent pedicle, the future abdominal pedicle, and here the mesoderm lining the chorion and that found in the embryonal formation unite (Figs. 26, 27).
Fig. 26. — Longitudinal section through Pig. 25, ovum v.H. of Spee. V.V., the future umbilical vesicle. The adherent band of mesoderm connects the embryonal formation with the extra-embryonal membrana chorii.
Fig. 27. — Pig. 26 enlarged, showing actual conditions in the ovum v.H. pictured schematically in Pig. 19a. U.V., the future umbilical vesicle ; ENT., entoderm ; HES., mesoderm.
Fig. 28. — Transverse section through germinal plate of Figs. 26 and 27 (Spee.)
Posterior to the caudal knot of the germinal plate, the umbilical vesicle sends a prolongation, the allantoic duct, into the abdominal pedicle, which duct is separated from the caudal side of the amnion by mesoderm. It is relatively long and probably formed early. It is through the adherent band of mesoderm that the vessels of the fetus pass to the chorionic membrane and into the villi.
The caudal knot of the primitive streak region forms the abdominal pedicle. The germinal plate is only a portion of the completed primitive streak region. There is as yet no differentiation into medullary plates or chorda. The germinal plate has its dorsal surface toward the point of union of the abdominal pedicle to the chorion and its long axis runs radially to the chorion. It is of oval form and has a median furrow on its dorsal surface. Its dorsal surface follows, in addition, the curve
Fig. 29. — Change from Fig. 27, showing ventral curve due to growth in length of germinal plate. (Schematic.) M, mesoderm.
Fig. 29a. — Stage of still further growth of cephalic end of germinal plate. Embryo Gle of Spee.
of the amniotic cavity and is therefore concave. Its dorsal furrow lies in the same plane as the lumen of the allantoic duct, and its caudal portion is at right angles to the duct. It consists of high cylindrical cells, highest at the middle (Fig. 28). Laterally it extends on into the amniotic lining. Laterally, ectoderm and mesoderm are separated by a membrana prima, which is always present between parallel layers of mesoderm and ectoderm. In the median line, however, is a fibred, granular substance, and here possibly a connection between ectoderm and mesoderm existed. A characteristic connection at the region of the primitive streak is present in mammalia and in older human embryos. There is probably no connection between mesoderm and entoderm, and in the next embryo there is no layer continuity between mesoderm and entoderm posterior to the canalis neurentericus.
Fig. 29b. — Embryo Glc of Spee. A, amnion cavity. X, between ectoderm and entoderm mesoderm comes. All anterior to the canalis neurentericus is new as compared with embryo v.H., Fig. 27.
It is to be noted that in Fig. 27 the germinal plate has a dorsal curve. The next stage is represented by a ventral curve (Fig. 29). As a result of this (1) the mesoderm between the germinal plate and the entodermal vesicle, and (2) that part of the entodermal vesicle lying parallel to the germinal plate hecome included in the ventrum of the curved germinal plate and form the mesoderm and entoderm of the fetus. The actual change is seen in Fig. 29 a and o.
2. The next older embryo (Gle) shows that the new growth concerns the addition of new elements to the germinal plate, plus an increase in the size of the amniotic cavity and the umbilical vesicle (Fig. 29&). ,The primitive streak region*in v. H. has grown a little, but keeps its position approximately. The mesoderm of the abdominal pedicle, the allantoic duct, and the caudal part of the primitive streak region remain about the same. In their growth a pause ensued, which pause continues until the embryo has seven primary vertebra?. Therefore the added growth concerns the cranial end of the germinal plate, while the caudal end remains a fixed point. The anterior part of the germinal plate has grown to four times the size of that in v. II., with the result that it extends almost at right angles to the original germinal plate, because the caudal end remained a fixed point and thus caused a transposition of the cranial area of the germinal plate. Thus the umbilical vesicle and amniotic cavity are pushed away from their position near the chorion into the deeper part of the mesodermal slit. A continuation of this process causes the embryo eventually to lie with its ventral surface turned toward the point of adhesion of the abdominal pedicle. At the same time the umbilical vesicle has grown, too, so that the embryonal formation of Gle has added a growth almost as large as v. H. itself. In v. H. all those areas of the germinal plate are absent which in Gle turn their dorsal side to the chorion, that is, all cranial to a line drawn transversely through the canalis neurentericus (Fig. 295). The germinal plate, as a result of the rapid growth of the medullary plates, grows at right angles to the long axis of the primitive streak region of v. H. The primitive furrow has an S shape on the dorsal surface. The cranial end of the chorda formation bends ventrically and ends together with the anterior end of the medullary plate. Anterior to the canalis neurentericus the chorda entoderm and the medullary plate lie close together. At the anterior boundary of the canalis neurentericus the ectoderm bends into the area of the chorda entoderm and the latter possesses elements of the ectoderm.
Fig. 30. — The three layers of a human embryo, still without primary vertebrae. Transverse section. (Keibel.) Showing growth of lateral walls, which thus enclose the entoderm within them.
Fig. 30a. — The forming of the intestine. Schematic. (Kollmann.) The mesoderm is divided into a parietal and a visceral layer. The celom, or space between these layers, is the future peritoneum. Intestine and umbilical vesicle are connected by a narrow duct.
With the continued growth of the cephalic end and the consequently decided ventral curve of the embryo, as well as through the growth of the lateral walls, a portion of the entodermal sac lies within the embryo. The ectodermal germinal plate has on its ventral surface then a strip of mesoderm and upon this mesoderm a part of the very entoderm which lines the entodermal abdominal vesicle (Fig. 30). Anterior to the canalis neurentericus is found most of the embryo and the medullary farrow and plates. The embryo consists here of three layers.
Fig. 30b. — Human embryo, 2-4 millimetres long, with heart and abdominal vesicle removed and umbilical pedicle cut. (After His.) Showing connection between intestine and umbilical vesicle.
Fig. 30c. — Caudal end of embryo, 3 mm. long. Reconstruction. (Keibel.) CI., cloaca : Md.. medullary canal ; Seine, tail ; Schw. D., caudal intestine. Showing relation of allantoic duct to the cloaca.
Fig. 30d. — Embryo 296, with decided ventral curve, has turned so that the abdominal surface faces the adherent band. X, omphalo-enteric duct. The heavy black line about A, passing off from either end of the embryo, is the amnion. Int., Intestine. Umb. pes., umbilical vesicle. (Schematic.) The embryo now has its ventral surface turned toward the abdominal pedicle.
Posterior to the canalis neurentericus is the original primitive furrow with the primitive lateral plates. The embryo here consists, too, of three layers. The mesoderm of the posterior part goes over into the adherent mesodermal band, the future abdominal pedicle. At the anterior and posterior ends the ectodermal layer of the embryo goes over into the single-layered amnion.
The original cephalic and caudal ends of the embryo (the points where ectodermal germinal plate goes over into singlelayered amnion) develop decided ventral curves. So do the lateral walls or sides of the germinal plate. As a result, the abdominal vesicle becomes constricted more and more, and the wide connection of the abdominal vesicle with the entodermal area of the embryo is narrowed so that a constantly narrower portion connects the abdominal vesicle with the interior of the embryo (Fig. 30a). The portion in the embryo, the entoderm of the embryo, forms the intestine and the cloaca (Fig. 30 a and b. The cloaca is a sac into which intestine and allantoic duct enter (Fig. 30c). As a result the abdominal vesicle is connected with the intestine by what has become a narrow duct, the omphalo-enteric duct, while the allantoic duct situated in the adherent band enters the cloaca (Fig. 30d). It may be said, for the sake of a readier understanding, that the cloacal portion of the entoderm sends a prolongation, the allantoic duct, into the adherent band. (On the umbilical vesicle develop vessels, the omphalo-mesenteric vessels, which enter the mesentery of the intestines, while the omphalo-enteric duct enters the intestine near the future cecum.) Later the cloaca becomes divided into a posterior part continuous with the intestine, the rectum, and an anterior part, or bladder, continuous with the allantoic duct, the future urachus.
Fig. 30e. — External scheme of embryonal formation, caudal end, with amnion removed, showing relative situation of parts. A combination of Figs. 29b and 30c. (Waldeyer.)
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Reference: Bandler SW. Uterine and tubal gestation. (1903) William Wood & Company, New York.
Cite this page: Hill, M.A. (2021, April 12) Embryology Book - Uterine and tubal gestation (1903) 1-7. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Uterine_and_tubal_gestation_(1903)_1-7
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