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neurêl tîssue wíth mesoderm however was maintained at the sites of
myelodysplasias because of the encroachment of somitic mesoderm dorsaj
to the I es ions .
The most marked cystlc and hemorrhagic. changes extended from the
postbrachlal area to the caudal region and were a:íociated with defective
mâturatîon of the tail-bud. The embryo wìth ãmyel ìa (4Zf 6!) provided
the most extreme example of this process, with hemimyelia of the crural
regîon, amyel ia of the postcrural region, and loss of all recognîzable
structures în the cauda! region.
The embryo with diplomyel ia (42E 56) simllarly showed hemimyelia in
the postbrachiaì, crural and postcrural regions, giving way to d¡plonryel
ia in the caudal region assoclated ùrith the persistence of accessory
cana I s.
ln the slngle embryo showing both myeloschlsis and myelodysplasia
(428 21'r, ê rather smal I cord în the postbrachial region gave bray to an
everted myetoschisis (showing wide separation from the notochord) and
then ên exposed dysplastîc plaque (in contact with notochord) at the crural
region. There was a smal I irregular mass of uncanalized neural tlssue
(covered by ectoderm and somitic mesoderm across the midline) ín the postcrural
regfonl and amyelia in the caudal region. Neural. pìate and taÌlbud
materials were not clearly separated at the êrea of myeloschisis.
6.3.9 BgyjeU pt Histologîcal Changes in Experimenral Embrvos
A review of the histological features descríbed in Sectíon 6.3
revealed certain dlfferences between experimental and control embryos ln
each g roup.
ln the regions of myeloschisîs or myelodyspìasia experimental embryos
showed varlous changes which appeared to be assoclated consistently with
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