Paper - On the pineal region in human embryos
|Embryology - 24 Jan 2020 Expand to Translate|
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Warren J. On the pineal region in human embryos. (1917) Anat. Rec, 11: 428-429.
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On the Pineal Region in Human Embryos
Harvard Medical School. (1917)
Presented at the 33rd Meeting of the American Association of Anatomists in New York (Dec 27-29, 1916).
The object of this communication is to call attention to three special features in the development of the pineal region in human embryos.
1. The primary archesin the roof of the forebrain
In an embryo of 10 mm all these arches are clearly differentiated. A low velum separates a well marked paraphysal arch from a relatively short and thick-walled post velar arch. The epiphysal arch is sharply defined with also rather thick walls and is succeeded by a relatively long pars intercalaris. This part of the brain roof forms a low arch in the posterior end of which the posterior commissure can be seen. The commissure seems to appear in this portion of the forebrain before invading the roof of the midbrain. In an embryo of 15 mm the arches are more fully developed. A slight median thickening in the paraphysal arch marks the anlage of the paraphysis. The posterior commissure now occupies a larger part of the pars intercalaris and has developed backward into the midbrain. The primary arches as first described by Professor Minot in Acanthias can therefore be demonstrated in human embryos and in addition the pars intercalaris forms an arch of relatively great length as compared with its appearance in lower vertebrates.
In the embryos of the Harvard Collection the earliest trace of the paraphysis can be noted as a slight thickening in the paraphysal arch in the embryo of 15 mm mentioned above and in two others of 16 mm No traces could be found however in any of the embryos of from 17 to 22 mm with the possible exception of one of 19 mm. In an embryo of 23 mm sagittal series it appears as a tiny hollow elevation similar to its earliest form in lower vertebrates. In another embryo of 23 mm transverse series it is a little larger and in one of 25 mm it forms a good sized oval outgrowth with a cavity opening into that of the brain in front of the velum. Above this stage it could be demonstrated in an embryo of 31 mm as a mere tiny elevation and also in one of 36 mm where there was a slight cavity attached by a solid stalk to the brain wall. The oldest embryo in which any trace could be made out was one of 44.3 mm where a tiny conical elevation in the paraphysal arch was all that could be seen. The paraphysis therefore does exist in certain human embryos but it is a rudimentary and inconstant structure. A short but well defined paraphysal arch could be followed in all the embryos studied.
3. Post velar arch
A complicated prolongation of the anterior end of this arch just, behind the velum forms a striking feature in many embryos. This outgrowth appears either as a median projection or as a bilateral formation on either side of the median line coming into intimate relation with the vessels over the brain roof. As the outgrowth becomes more complicated, tubules are given off in a rather bewildering manner, which may become detached and appear as blind vesicles buried in the midst of this tubular formation. The paraphysis is more or less covered by this projection which overhangs to a large extent the paraphysal arch. The formation begins in embryos of 23 mm as a simple median outgrowth. In an emryo of 25 mm the outgrowth is a double one. In an embryo of 31 mm two closed vesicles can be seen on either side of the middle arch, but still in contact with the brain wall. In an embryo of 36 and 44 mm where the formation is extremely complex, one or more of these vesicles are found completely detached from the brain. Their walls are usually thinner than those of the other tubules among which they lie. Attention is called to this formation especially to the vesicular portion as it is such a striking feature in all the embryos from 23 mm up to 44 mm.
Cite this page: Hill, M.A. (2020, January 24) Embryology Paper - On the pineal region in human embryos. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Paper_-_On_the_pineal_region_in_human_embryos
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