Paper - Observations upon Young Human Embryos: Difference between revisions

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==Second Embryo "H 98"==
==Second Embryo "H 98"==
==LIST OF REFERENCES.==
==EXPLANATION OF PLATES I.-III. FIGS. 1-6==
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{{Glossary}}
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Revision as of 00:16, 21 February 2012

James Thomas Wilson

Challis Professor of Anatomy in the University of Sydney, Australia.

Medicine Museum

<pubmed>17233002</pubmed>| PMC1288949


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Part 1

The appearance in recent years of Keibel and Mall's Manual of Human Embryology (1), following upon Keibel and Elze's Normentafein (2), marked an epoch in the formulation of our knowledge of specifically human development.


The comprehensive summary there offered of our knowledge of the earlier human ontogenetic processes provided for the firsttime a more or less connected account of these phenomena, but it also served to accentuate the still very sketchy and incomplete character of that knowledge.

Much of our belief in regard to the method of establishment of the human blastocyst is stil quite hypothetical, even if probable; and as regards the appearance of the earliest rudiments of the body itself, our knowledge isbased on a very few human specimens separated by intervals which it is important to fill in with the aid of intermediate or allied stages.

In the present paper I propose to give an account of the three youngest human embryos in my collection.


Previous writers have described and figured specimens of a stage of development more or less similar to those exhibited by the two older of the embryos which form the subject of this communication. Nevertheless, well-preserved specimens, of ages nearly corresponding to these, are of such comparative rarity that for some time to come it will still be desirable to have accurate records published of the form and structure of any that may become available for detailed examination. As a matter of fact, no two specimens hitherto described, however apparently similar in stage of development, have proved to be precisely identical in detail. It will appear in the course of the paper that each of the individual embryos under consideration presents features entitling it to independent description.


A more special interest attaches to the youngest of the three specimens, inasmuch as it would seem to exhibit a phase of development hitherto unrepresented in the records of early human embryos.


It possessed probably two, possibly three, pairs of somites, and may thus be determined as occupying a position in the gap between stages 2 and 3 of Keibel and Elze's Norrnentafel. These stages are represented respectively by Spee's embryo " Gle " (3), and the Kroemer-Pfannenstiel embryo " Klb."


Hitherto, or as far as I am aware, no human embryo has been recorded as exhibiting a smaller number of somites than five (in " Klb ").


I am inclined to believe that the embryo "E,"No.1 of His 'Normentafel (4), would have turned out to be of very similar character to that now about to be described, inspire of the somewhat greater length of the former (21 mm. as against 1-68 mm.).


(truncated)

History of the Human Embryo "H3"

Characters and Dimensions of Chorionic Vesicle

Micrometer Measurements

Form and Characters ofEmbryo and itsAppendages

Mesodermal Somites

Chorda

The chorda is still in the stage of intercalation in, and is indistinguishable from, the entoderm.

Excretory Apparatus

There is no ascertainable pronephric rudiment, nor would one expect to find any at this early stage. In any case, the histological conditions are unfavourable to any critical verification.

Medullary Plate

The general characters of the medullary plate have already been alluded to in connexion with the form of the embryo.

Absence of Sense Organs

There is no trace whatever of optic groove formation nor of auditory areas, although there is a diffuse and rather extensive thickening of the head ectoderm in the posterior cephalic region, which may possibly foreshadow the appearance of such areas.

Oral Region

On the ventral aspect of the head, immediately in front of the line of reflexion of the ectoderm from the free head to the "pericardial plate" swelling (text-fig.1), the ectoderm forms a plate, slightly recessed bilaterally, the depressions being separated from one another by a slight median prominence.


Atlimentary Canal

The fore-gut shows a general agreement in character with that of the important Kroemer-Pfannenstiel embryo "Klb" of Keibel and Elze's Normentafel.

Allantoic Duct

The proximal portion or vestibule of the allantoic duct has already been referred to, as also its continuation into a narrow canal of uniform calibre prolonged not the reflexed body-stalk.

Pericardum

The pericardium lies chiefly ventral to the pharynx, but it extends for a distance of about 005 mm. in front of the cranial limit of the later.

Heart

The heart itself is still almost completely duplex as regards not only its endothelial but also its myoepicardial components.

Summary of Characters of Embryo "H3"

Second Embryo "H 98"

LIST OF REFERENCES.

EXPLANATION OF PLATES I.-III. FIGS. 1-6

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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)

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Cite this page: Hill, M.A. (2024, March 29) Embryology Paper - Observations upon Young Human Embryos. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_Observations_upon_Young_Human_Embryos

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G