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Fig. 8. Photomicrograph from section 24 of H951 (17 somites)

Showing the site of the anterior neuropore. Zeiss apo. imm. 'X ,’ Homal III. X 700.

The section cut through about the middle of the site of the closing anterior neuropore is shown in figure 8. It is to be noted there that the surface epithelium is greatly thickened in the middle as a wedge-shaped plug of cell mass filling up the gap between the lips of the neural folds. The arrangement of cells there gives the impression that they are piled up one layer upon another, with exceedingly flattened cells on the outer surface, spindle—shaped in the intermediate layer, and two to three round cells in the innermost stratum. Under a higher magnification, the flattened cells of the outermost layer appear to be but cytoplasmic processes thrown across the midline to form a bridge between two sides; whereas the cells lateral to this region begin to assume definite forms arranging from elongated epithelial to low cuboidal cells. Next to this layer the cells, which are really not clearly demarcated from the layer just described and the one to be dealt with presently, but arbitrarily divided according to their shape for descriptive purposes, are arranged in an obliquely directed radiation toward the midline. This radial arrangement gives place to a few round cells with oval nuclei, bounding the ventricle. This type of cellular arrangement is responsible for the conical appearance of the cell mass on cross-sections. Now, turning to the neural epithelium, the neural folds have not yet fused and the arrangement of cells is clearly marked as contrasted with that of the head epithelium. But at the tip of the right neural lip (fig. 8), where the head ectoderm is continuous with the neural epithelium, the cells of the former bend inward upon the latter to form the brain wall. Tracing the sections forward (cephalic to fig. 8, i.e., ventral in fig. 5), it is seen that the lips of the neural fold gradually approach each other and then fuse. The plug of the head ectodermal cells in the meantime changes from its radial conical arrangement into an irregular cell mass between the flattened head epithelial cells and the epithelium of the neural tube, until it is completely separated from the nervous tissue. Now, let us proceed with the examination of sections immediately caudal to figure 8 (i.e., dorsal in fig. 5); the ectoderm and neural folds cannot be separated, the former still indicating an inward bending upon the latter to form the brain wall. Still caudal to these sections, the neural tube becomes closed by the joining of the two lips of the neural fold, and the head ectoderm is distinctly separated from the neural epithelium.

Abbreviations for all Figures
  •, internal carotid artery
  • A.seg.dor., dorsal segmental arteries
  • A.urnb.d.-s., umbilical artery, right, left
  • All., allantois
  • Am., amnion
  •, aortic anastomosis
  • Ao.dor.d.-s., dorsal aorta, right, left
  •,I, II, aortic arches, right, left, I, II
  • Area br.III,IV, ectodermal areas of third or fourth visceral pouches
  • Area hy., ectodermal area of hyoid arch
  • Area P prin., principal trigeminal area (or the ectodermal area of placodal contributions)
  • Area mand., mandibular area
  • Area ophth, ophthalmic area
  • Atr.d.s., atrium, right, left
  • Atr.canal., atrial canal
  •, internal gill rudiment, right, left
  •, aortic bulb
  • Bulb.cor., bulbus cordis
  • Ch.dor., chorda dorsalis
  • Ch.sp., chorda spinalis
  • Coel., coelom
  • Coel.epith., coelomic epithelium
  • Coel.per., pericardial coelom
  • Cor, site of heart
  • Cr.neur.V, trigeminal neural crest
  • Cr.neur.VII—VIII, acousticofacial neural crest
  • Cr.neur.IX—X, glossopharyngeal vagal neural crest
  • Dien., diencephalon
  •, discus incepts
  • Disc.V, trigeminal area where the ectoderm fused with the underlying tissue (neural crest?)
  • Disc.VII, facial epibranchial placode
  • Disc.IX, glossopharyngeal epibranchial placode
  • Disc.X, vagal epibranchial placode
  • Duct.proneph., pronephric duct, primary excretory duct
  • Ect., ectoderm
  • Endocard., endocardium
  • Ent., entoderm
  • Pos.pre-op., preoptic fossa
  • Hep, primordium of liver (both medial and lateral thickening)
  • Inf., infundibulum
  • Int.caud., hindgut
  • Int.atr.sul., interatrial sulcus
  • Isth., isthmus
  •, II, III, first, second or third branchial membranes.
  • Memb.buc., buccopharyngeal membrane
  •, cloacal membrane
  • Meschy., mesenchyme
  • Mesen, mesencephalon
  • Myocard., myocardium
  • Neph., nephrostome
  • Neu.ant., anterior neuropore
  • Ph., pharynx
  •,2, ventral pharyngeal fold, right, left, first, or second
  •, anterior intestinal portal
  • Pr.pul., primordium of lung
  •, prechordal plate
  • Prosen., prosencephalon
  • Proc.mand., mandibular process
  • Prom.cor., heart swelling (Davis)
  •, 2, etc., first, second, etc., presegmental aortic branch
  •, lateral aortic branch
  •, ventral aortic branch
  • Res.pre.op., preoptic recess (Johnston)
  • Rh.1, .9, 3, 4, 5, 6, 7, rhombomere 1, 2, 3, 4, 5, 6, 7
  • S.1,2, etc., first, second, etc., somite
  • S.ven., sinus vesous
  •, II, III, first, second, third pharyngeal pouch
  • Sac.vit., yolk sac
  • Sect, section
  •, septum transversum
  • Sul.di-mesen., dimesencephalic boundary
  •, laryngotracheal sulcus
  • Sul.op., optic sulcus
  • Tel., telencephalon
  • Thy;., primordium of thyroid gland
  • Tor.op., torus opticus (Froriep)
  • Tub.proneph., pronephric tubule
  • V.cap.prim., primitive head vein
  • V.card.ant., anterior cardinal vein
  •, common cardinal vein
  • Vent.cord., ventricle of heart
  • Ves.mesoneph., mesonephric vesicle
  • Ves.op., optic vesicle
  • Ves.ot., otic vesicle
  • Ves.proneph., pronephric vesicle
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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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Wen IC. The anatomy of human embryos with seventeen to twenty-three pairs of somites (1928) J. Comp. Neural., 45: 301-376.

Cite this page: Hill, M.A. (2024, May 28) Embryology Wen1928-Fig08.jpg. Retrieved from

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