1987 Developmental Stages In Human Embryos - Stage 10
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O'Rahilly R. and Müller F. Developmental Stages in Human Embryos. Contrib. Embryol., Carnegie Inst. Wash. 637 (1987).
| Online Editor Note |
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| O'Rahilly R. and Müller F. Developmental Stages in Human Embryos. Contrib. Embryol., Carnegie Inst. Wash. 637 (1987).
The original 1987 publication text, figures and tables have been altered in formatting, addition of internal online links, and links to PubMed. Original Document - Copyright © 1987 Carnegie Institution of Washington.
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- 1987 Stages: Introduction | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | References | Appendix 1 | Appendix 2 | Historic Papers | Embryonic Development
| Historic Disclaimer - information about historic embryology pages |
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Stage 10
- Approximately 1.5–3 mm in length
- Approximately 22 ± 1 postovulatory days
- Characteristic feature: 4–12 pairs of somites
Summary
External: 4–12 pairs of somites; fusion of neural folds is imminent or in progress; the optic sulcus may have appeared; pharyngeal arch 1 begins to be visible on the surface.
Internal: the cardiac loop is appearing; the laryngeotracheal sulcus develops; the intermediate mesoderm becomes visible.
Size and Age
The chorion generally has a diameter of 8–15 mm. The greatest length of the embryo, although not of great informational value (Bartelmez and Evans, 1926), is usually 1.5–3 mm.
The age is approximately 22 postovulatory days. A brief review of stage 10 was published by Heuser and Corner (1957), and a detailed investigation of this stage was undertaken by Müller and O'Rahilly (1985), who provided graphic reconstructions. Both of these publications contain an appropriate bibliography.
External Form
(figs. 10-1 and 10-2) The criterion for stage 10 is the presence of 4–12 pairs of somites. This stage is particularly important because, during it,the neural tube first begins to be formed from the neural folds and groove. In the less advanced specimens the neural groove is open throughout its whole length, whereas by the end of the stage the groove is closed from the rhombencephalon to below the level of the last somites present.
The embryo is becoming longer, and the umbilical vesicle continues to expand. The rostral portion of the neural folds becomes elevated, a caudal fold begins to appear, and the whole embryo comes to rise beyond the level of the umbilical vesicle (i.e., a variable degree of lordosis usually becomes evident). By the end of the stage the cardiac region has become a prominent feature of the external form (Boyden, 1940).
Representative specimens of this stage are illustrated in figures 10-3 and 10-4. These outlines, showing the dorsal aspect of a median section of each specimen, are enlarged to the same scale. As pointed out by Bartelmez and Evans (1926), the mesencephalic flexure is present in all embryos of this period. A dorsal flexure may or may not be found. The curvature of the dorsal profile varies from a gentle convexity through all degrees of concavity (lordosis) from the least possible curve to a deep, sharp kink. Bartelmez and Evans (1926) and Streeter (1942) have discussed the significance of this variation as seen in human and rhesus embryos of early somitic stages. On the whole, the evidence indicates that, whereas extreme dorsal flexion should be regarded as an artifact, anything from a gentle convexity to a moderate dorsal concavity can be considered normal.
The optic sulcus develops in the forebrain and, toward the end of the stage, an indication of invagination of the otic disc is found. During stage 10, swellings begin to appear for the mandibular arch (Politzer, 1930, fig. 5), and the hyoid arch and probably the maxillary process become identifiable (Bartelmez and Evans, 1926, fig. 6). Pharyngeal cleft 1 becomes visible (Corner, 1929, figs. 4 and 10).The future ectodermal ring (O'Rahilly and Müller, 1985) is beginning to form as a thick area overlying pharyngeal arch 1. An indication of an intermediate band is present and represents the future intermembral part of the ectodermal ring.
Closure of the neural groove occurs first during stage 10, in embryos of approximately 5 paired somites. The site of initial closure appears to be rhombencephalic (part D) or upper cervical, or both. It seems that closure may soon occur in several places independently, so that the process is not entirely comparable to a zip fastener. The maximum limits of closure found are to rhombencephalon 1 rostrally and to the level of somites 15/16 caudally. The caudal extension of the closure proceeds at about the same rate as the formation of new somites (Bartelmez and Evans, 1926), so that the margin of the caudal neuropore is usually opposite the latest pair of somites. Rostrally, progress is slower and apparently more variable.
The neural plate in stage 9 extends caudally to the level of the neurenteric canal. In stage 10 differentiation into neural plate extends beyond that landmark, as indicated by a radial arrangement of cells and separation from the underlying primitive streak by a basement membrane. The transition to the more caudally situated, undifferentiated ectoderm is gradual.
Cytoplasmic inclusions in the developing nervous system have been noted by several authors and have frequently been considered to indicate degeneration. Such inclusions are found in a number of areas, including the apices of the neural folds, the primitive streak, and the prechordal plate.
The histological features of neurulation have been investigated (Müller and O'Rahilly, 1985). In the spinal region, the neural folds approach each other and the surface ectodermal cells of the two sides make contact while a gap remains between the neuro-ectodermal cells of the two sides. Where fusion of the surface ectoderm and of the neuro-ectoderm has occurred across the median plane, a wedge-shaped area of neural crest is present in the dorsalmost part of the neural tube. Protoplasmic processes then protrude, and crest cells emerge from the tube. A more or less similar appearance of wedge-shaped neural crest and migrating cells is found also in part D of the hindbrain. Further rostrally in the hindbrain, and also in the midbrain and the forebrain, at the apices of the open neural folds, neural crest cells are emerging from the neurosomatic junction and also from the adjacent neural ectoderm in areas where the basement membrane is deficient. At the mesencephalic level, preparation for fusion is occurring. The surface ectoderm protrudes more medially, thereby overhanging the neuro-ectoderm. Certain intermediate areas that are still open have been misinterpreted as neuroschisis. The neural folds show a high alkaline phosphatase activity (Mori, 1959a). It is important to note that differences in the process of neurulation have been recorded in various species.
Neural Crest
The neural crest continues to develop during stage 10 when, in the head, it probably reaches its peak. The rostral (mesencephalic) and facial portions are constantly present. The crest material for the superior ganglion of the vagus appears before that for the glossopharyngeal. The probable succession of appearance is: facial, rostral (mesencephalie), trigeminal, vagal, occipital, and glossopharyngeal. The facial crest is the most conspicuous. In the area of the vagal crest, the neural crest material is clearly joined by cells of the surface epithelium in some of the embryos. The otic plate, at least in some instances, may be seen to contribute cells to the facial (acousticofacial) crest. The cells of the neural crest appear to be derived from the open neural plate at the neurosomatic junction, mostly in areas where the neural tube has not yet formed. Apart from its formation of cranial ganglia, the neural crest migrates into the head mesenchyme and is believed to contribute to the skull and face. Illustrations purporting to show precisely the extent of the contributions in the human (based on the chick embryo) are quite unwarranted in the present state of knowledge.(1) The proposal of failure of crest cell formation as a facial pathogenetic mechanism has been disputed. Neural crest cells clearly leave the neural plate at areas where the basement membrane is interrupted. After closure of the neural groove in stage 10, neural crest still seems to be derived from the neural ectoderm, although a simultaneous origin from the surface ectoderm cannot be excluded.
(1) It has frequently been pointed out that the “static” appearances seen in serial sections cannot justifiably be used for the interpretation of “dynamic” processes. It has less frequently been emphasized that there are equally grave problems in assuming that the results of experimental embryology can be transferred without more ado to the human embryo.
Eye
By approximately 7–8 paired somites the neural folds of D1 consist of thick neural ectoderm that comprises the optic primordium. Identification of the optic primordium is difficult, and reconstructions are necessary. The thickened area, which contains many mitotic figures and cytoplasmic inclusions, continues across the median plane as the chiasmatic plate (primordium chiasmatis). A more or less indented area in D1 represents the optic sulcus (fig. 10-7). In contrast to the shallow ventricular surface in D1, the ventricular surface in D2 is convex and represents the future thalamic area of the diencephalon. The optic sulcus does not always reach the median plane, but, when it does so, it indicates the future postoptic recess (Johnston, 1909). The area rostral to the optic primordium on both sides of the terminal notch represents the telencephalic primordium (fig. 10-7B). Some of the earlier specimens in which an optic primordium or sulcus has been described are unfortunately not of sufficient histological quality to avoid the suspicion that artifacts are present. Moreover, the plane of section is of the utmost importance in the identification of the optic region. D2 gives rise later to the thalami, but it is not correct to state that “the entire dorsal thalamic wall... had originally been incorporated in the optic evaginations” (Bartelmez and Blount, 1954). Careful plotting of the optic sulcus in the Payne embryo shows that it is confined to D1 and is transverse in direction, in contrast to the vertical markings shown by Payne (1925, fig. 2). Similarly in the Corner embryo, the optic sulci (which do not quite meet in the median plane) are limited to D1, and the optic primordia (i.e., the surrounding thickenings) occupy more or less the whole of D1. The lateral limit of each optic sulcus appears to be beginning to extend caudally. Corner (1929, fig, 1) plotted the sulcus more caudally, probably because of the influence of the early interpretations of Bartelmez (1922). An improved plotting of the Corner embryo was illustrated by Bartelmez and Dekaban (1962, fig. 67), although the midbrain was placed too far rostrally, thereby not allowing adequately for D2. By the end of stage 10, the optic sulci extend more caudally, as in the Litzenberg embryo (Boyden, 1940, fig. 13), in which the label superior colliculus should read thalamic primordium in D2.
Ear
The otic plate in at least one embryo contributes cells to the facial (or faciovestibular) neural crest. Such a contribution continues to at least stage 12 (O'Rahilly, 1963). It may be that the non-neuronal cells in the vestibular and cochlear ganglia are derived from the neural crest.
Specimens of Stage 10 Already Described
- 4 somites, Carnegie No. 3709 (University of Chicago H 279). Characterized with outline sketches, by Bartelmez and Evans (1926).
- 4 somites, Histologisch-Embryologisches Institut, Embryo A, Vienna. Fully described by Sternberg (1927).
- 4 somites, Histologisch-Embryologisches Institut, Embryo Ca, Vienna. Fully described by Orts Llorca (1934).
- 4–5 somites, Florian's Embryo Bi II. The whereabouts of this, the following embryo, and the 10-somite Bi XI (see below) are not known; Florian's collection has not been found since his untimely death during World War II. The embryo Bi II was briefly characterized by Studnicka (1929), cited and partly illustrated by Florian (1928, 1930a).
- 4–5 somites, Florian's Embryo Bi III. (See note on previous embryo.) Briefly characterized by Studnicka (1929) and cited by Florian (1928).
- 4–5 somites, Carnegie No. 2795. Cited and briefly characterized by Bartelmez and Evans (1926). The specimen is distorted and somewhat macerated.
- 5 somites, Anatomisches Institut, Zürich, GM 1954. Described and illustrated by Schenck (1954).
- 5 somites, No. 103, Department of Anatomy, Tohoku University, Sendai. Distribution of alkaline phosphatase studied by Mori (1959a) in this and in another (No. 101), possibly 8-somite, embryo.
- 5–6 somites, Pfannenstiel “Klb” (originally at Giessen; was in Keibel's Institute at Freiburg i. Br. about 1911, may now be in Berlin). This well known embryo is No. 3 in the Keibel and Elze Normentafel (1908). Models by Kroemer (1903). A partial set of tracings made by H. M. Evans is in the Carnegie Collection, No. 5463.
- 6 somites, Carnegie No. 8244. Somewhat distorted; histologically fair.
- 6 somites, University of Michigan No. 71, Ann Arbor. Briefly described by Arey and Henderson (1943). A full description in an unpublished doctoral dissertation is in the files of L. B. Arey at Northwestern University, Chicago.
- 6 somites, Carnegie No 8818 (University of Chicago H 338) Pathological, not used in present study. Listed here because cited by Bartelmez and Evans (1926).
- 6–7 somites. His’s Embryo “SR.” Cited by His (1880) and by Bartelmez and Evans (1926). Has been studied only in the gross.
- 6–7 somites, Embryo LM (present location unknown). Cited here from manuscript notes at Carnegie laboratory, made from Russian text of Burow (1928). Condition said to be poor.
- 7 (?) somites, Embryo “Ludwig,” Berlin. Described by Streiter (1951). This specimen, which is somewhat macerated, is in certain characteristics considerably in advance of others of similar somitic number.
- 7 somites, Carnegie No. 6330 (University of Chicago H 1404). Extensive manuscript notes on this specimen, made under the supervision of G. W. Bartelmez, are in the files of the Carnegie laboratory.
- 8 somites, Carnegie No. 4216. Described by Payne (1925), and very frequently cited.
- 8 somites, Dublin. Described by West (1930); see also Arey (1938). Photographs and models are in the Carnegie Collection, No. 4923. Bartelmez (personal communication) thinks that this distorted embryo had only 5–6 somites.
- 8 somites, Carnegie No. 391. Described by Dandy (1910) and frequently cited (cf. Bartelmez and Evans, 1926, with additional illustrations). There were neither camera drawings nor photographs of the intact specimen, and therefore the reconstructions are not entirely satisfactory. The plaster models now at the Carnegie laboratory were made by O. O. Heard under the supervision of Bartelmez for the paper by Bartelmez and Evans (1926). The apparent lack of fusion of the neural folds described by Dandy is an artifact produced by a crack.
- 8 somites, Carnegie No. 1201 (University of Chicago H 87). Described briefly by Evans and Bartelmez (1917); cited, with illustrations, by Bartelmez and Evans (1926).
- 8 somites, Embryologisches Institut, Embryo Ct, Vienna. Fully described by Politzer (1930). Arey (1938) counts 8 paired somites in this embryo instead of 7 as stated by Politzer.
- 8 somites, University of Cambridge, Department of Anatomy H 98. Photographs and models in Carnegie Collection, No. 7251. Described by J. T. Wilson (1914). Cited by Bartelmez and Evans (1926), who consider it slightly abnormal in form although good histologically.
- 9 somites, Embryo “Esch I,” Marburg. Elaborately described by Veit and Esch (1922), and cited, with illustrations, by Bartelmez and Evans (1926), who count 9 somites instead of 8 as stated by the original authors. Chorionic villi studied in detail by Ortmann (1938). Photographs and models are in the Carnegie Collection, No. 4251.
- 9 somites, Embryo “Du Ga,” Geneva. Described by Eternod (1896); models by Ziegler were distributed commercially. Cited by Bartelmez (1922) and Bartelmez and Evans (1926), with illustrations. Tracings made by H. M. Evans at Geneva and models are in the Carnegie Collection, No. 4439.
- About 9 somites. Embryo Unger, Keibel Collection, Freiburg i. Br., No. 4 of Keibel and Elze (1908). Listed by Bartelmez and Evans (1926).
- 9 somites, Embryo “Jacobsen,” formerly at Kiel (Graf Spee's collection was destroyed in World War II). Described by von Spee (1887). Listed by Bartelmez and Evans (1926) as having “at least” 9 somites.
- 9 somites, Embryo Ca of Orts Llorca, Madrid. Various details described by Mari Martinez (1950) and Martinez Rovira (1953).
- 9–10 somites, Embryo R. Meyer 335. (Robert Meyer's collection was purchased by the late Hedwig Frey and bequeathed by him to the Anatomisches Institut, University of Zurich.) Listed by Bartelmez and Evans (1926), and cited by Felix (1912).
- 10 somites, Da2, Anatomical Institute, Basel. Described by Ludwig (1929). Plastic reconstructions. Neural groove closure extends rostral to otic discs.
- 10 somites, Carnegie No. 5074 (University of Rochester H 10). Fully described by Corner (1929), and subjected to volumetric analysis by Boyden (1940). Excellent specimen.
- 10 somites, Grosser's Embryo Schwz (present location unknown). Briefly described, without illustrations, by Treutler (1931). Preservation said to be not altogether satisfactory.
- 10 somites, Florian’s Embryo Bi XI. (See note on Bi II above.) Briefly described, with illustrations, by Politzer and Sternberg (1930); cited and partly illustrated by Florian (1930a).
- 10 somites, Anatomy Department, University of South Wales, Cardiff. Partly described and illustrated by Baxter and Boyd (1939).
- 11 somites, Embryo T 152, University of Toronto, Department of Anatomy. Cited by Arey (1938).
- 11 somites, Embryo G-dt, Uppsala. Described by Holmdahl (1943) as having 11 well-differentiated pairs of somites, with beginning delimitation of 4 more.
- 11–12 somites, Carnegie No. 8970 (University of Chicago H 637). Somewhat damaged. Cited, with illustrations, by Bartelmez (1922) and Bartelmez and Evans (1926).
- 12 somites, Carnegie No. 3710 (University of Chicago H 392). Cited by Bartelmez (1922) and Bartelmez and Evans (1926).
- 12 somites, Carnegie No. 3707 (University of California H 197). “Legge embryo.” Cited, with illustrations, by Bartelmez and Evans (1926). The coital history accompanying this specimen, which was declared to be reliable, would give it a postovulatory age of either 18 or 39 days; the former seems rather brief but the latter is much too long.
- 12 somites, Litzenberg embryo, University of Minnesota, Minneapolis. Briefly described by J. C. Litzenberg (1933); characterized and subjected to volumetric analysis by Boyden (1940), who counts 12 somites instead of 13–14 as in the original description. Photographs and model in Carnegie Collection, No. 6740.
- 12 somites, M. 24, University of Michigan, Ann Arbor. Cited by Arey (1938).
References
| Online Editor Note |
|---|
| O'Rahilly R. and Müller F. Developmental Stages in Human Embryos. Contrib. Embryol., Carnegie Inst. Wash. 637 (1987).
The original 1987 publication text, figures and tables have been altered in formatting, addition of internal online links, and links to PubMed. Original Document - Copyright © 1987 Carnegie Institution of Washington.
|
Search Pubmed
- 1987 Stages: Introduction | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | References | Appendix 1 | Appendix 2 | Historic Papers | Embryonic Development
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Cite this page: Hill, M.A. (2024, April 24) Embryology 1987 Developmental Stages In Human Embryos - Stage 10. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/1987_Developmental_Stages_In_Human_Embryos_-_Stage_10
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