PubMed · 14838763
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
IU N KVITNITSKII-RYSKOV. [Ectodermal modifications of early pathologic human embryos].. https://pubmed.ncbi.nlm.nih.gov/14838763/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The caudal region of the trunk was reassessed in 52 serially sectioned human embryos of stages 8-23, 42 of which were controlled by precise graphic reconstructions. The following observations, new for the human, are presented. (1) The neurenteric canal is an important landmark because rostral to it the neural plate of stages 8, 9, and the main part of the notochord develop, whereas caudal to it the neural plate of stages 10-12 and the caudal portion of the notochord are formed. All somites at stages 9-11 and probably also at stage 12 arise rostral to the site of the neurenteric canal. (2) A 'chordoneural hinge' can be detected in stages 10 and 11, where the caudal part of the neural plate gives off cells that probably participate in the production of mesenchyme. (3) When apparent disappearance of the epiblast is used as a criterion, then the primitive streak seems to end during stage 9. (4) The caudal eminence, derived from the primitive streak and covered by ectoderm, forms at stage 10 caudal to the site of the former neurenteric canal and persists as a terminal cap to at least stage 14, although formation of mesenchyme continues in stages 15 to 17 or 18. (5) As the region rostral to the site of the neurenteric canal grows because of the development of somites, the caudal eminence is shifted caudally. (6) The caudal eminence is most active developmentally during stage 13, when most of the required (ca 6 out of 9) pairs of somites appear. (7) The eminence produces the caudal part of the notochord and, after closure of the caudal neuropore, all caudal structures, but it does not produce even a temporary 'tail' in the human. (8) A temporal overlap results between primary and secondary development in the caudal part of the notochord. (9) Primary development begins very early with the formation of the inner cell mass at stage 3, and includes the development of the somites rostral to the neurenteric canal, whereas secondary development, with the exception of the notochord caudally, commences at stage 12. (10) Primary neurulation lasts from stage 8 to stage 12, secondary from stage 12 to stages 17 or 18. (11) Secondary development and secondary neurulation are characterized morphologically by direct formation of structures (notochord, postcloacal gut, neural cord/neural tube) from mesenchyme.
Seven embryos of stages 10-16 (3-5 weeks) were studied for their external form by means of graphic reconstructions. This is the first systematic report on the general surface anatomy of the early human embryo. The brain has been described and illustrated in a previous publication, and the present article is concerned particularly with an important although neglected feature: the ectodermal ring, described by Schmitt [Morph. Arb., Jena 8: 236-303, 1898] and named by Blechschmidt [Funktionsentwicklung. I. Mechanische Gegenwirkungen. Musterschmidt, Göttingen 1948]. Late in stage 10, three longitudinal bands can be seen on the surface: somitic, intermediate, and lateral plate. The intermediate band, which partly overlies nephrogenic tissue, is the site of the future ectodermal ring, which begins as an inverted U at stage 11 and is completed caudally in stage 12. The ectodermal ring, which may well be an important example of epithelial-mesenchymal interaction, comprises six parts: (a) rostral part, containing the situs neuroporicus, and olfactory and lens discs; (b) pharyngeal part, the covering of the pharyngeal arches; (c) occipital and cervicothoracic parts, related at first to the four occipital somites and later to the cervicothoracic junction; (d) membral part, represented by a preliminary ectodermal thickening, followed within 2 days by the apical ectodermal ridge; (e) intermembral part, related at first to the underlying coelom, and mesonephric duct and ridge; (f) caudal part, containing the cloacal membrane and a temporary 'caudal ectodermal ridge'. It is stressed that the incorrectly named 'Milchstreifen' is merely the intermembral part, in which the mammary crest ('Milchlinie' or 'Milchleiste') appears 1 week later.
Explore the source record for details and available documents.