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

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Thus the embryos selected for serial sectioning were rearranged
and examined by developnentar stages rather than hours of incubation,
4.8.3 súbdivislón lrirö Rédións
Examlnation of the serial sectrons reveared marked differences in
the development of the neural tube, notqchord., and somites at dìfferent
levels of al I embryos.
Each group of embryos was thus subdivîded into regions of neurar
development on the basls of non-neural morphological markers. These
markers were - found to correspond quite closely to developmental changes
along the length of the neural tube.
Because of the striking changes between Stage 10 and Stage 20 the
regîons werê not identîcal in each group, but were ¿rranged to encomp¿rss
the same developmental areas. For this reason the rela.tive size of each
region varied in the embryos of different groups.
The most important non-neural marker was somite mesoderm, divided by
reg lons in to:
a) presomite regîon: grouped w¡th the brain region,because after rotatÌon
of the head fotd the two areas courd not be separated rrn obr ique sections
b) upper and lower somite regions: grouped together for lack of çlear
morphol og i ca I separatîon
c) protosom¡te regîon: with club-shaped protosomites showing líttle
separation into dermatome, myotome, and sclerotome
d) unsegmented mesoderm region: with loosely arranged mesoderm not con_
densed into protosot¡î te s
e) posterlor region: with developing notochord ( p rotonotocho rd) still
continuous wlth developing mesoderm and neural t¡ssue.