Universlty of Manitoba, ln Partîal Fulfiìlment - MSpace at the ...

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lrnplicated in the pathogenesls of nryeloschlsis. lt has to be concluded
that myeloschisis în the present series of chick embryos treated by
wlndowi.ng .arises by simple non-closure of the neural folds, representing
a fai I ure of neurulation.
The development of rrúélódvsolasia was not preceded by any characterístic
shape of the rhor¡bo ¡ d sînus, and did not occui befor. Stage 16. The neural
canal could not be traced ilrectly înto the leslon, and there was no
separat¡on ¡nto neural plate and tai l-bud mater¡als. l',lyelodysplasia dld
not coexist wlth an open rhombold sinus, and formed an lrregular open
defect in whole embryos at /2 hours.
ln serlal sectionsof myelodysplasia the neural tube at the upper
end of the lesion was triangular (due to reduced neural plate material),
giving way.to a narrowly-everted or f lat plague(derived from tail-bud
material, and partly covered by ectoderm). Caudally, there wês an
apparently normal neural tube (derived from tail-bud materlal), or a
disrupted region forming diplomyel ia or amyel ia. The myelodysplasia lesions
were partly covered by ectoderm, and nowhere so smoothly contínuous with
ectoderm as the myeloschisis lesions. l'lîtoses were not restricted to
the surface of the plague.
The notdchord was uniformly ¡n contact with neural tissue, except
in one embryo that showed a combinatíon of myeloschisis and myelodysplasia.
Somites în the area of myelodysplasia were reduced in volume, and often
reduced in densityrdue to a loose arrangement of cells suggesting edema.
ln some areas blood vessels were dflated., with hemorrhages into the local
mesoderm. l'lhere neural tissue was very reduced, the somites fused dorsal ly
lnto a slngle mldline mass. All myelodysplasia lesions showed reduction of
neural volume, both on lmpressidn and by measurement.