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

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6.3.5 staEe 13-16 córitról Embryos (Qroup lll)
All stage l6 control embryos showed complete neural closure, whereas
the stage l3 cont!'ol embryos were stlr crosing ât the posterior rhomboid
sinus. The overlap zone was fuly deveroped, with êccessory canals at the
unsegmented mesoderm and caudal areas, and recognizabre overrapping w¡thout
canals in the protosomite area. rhe rhombic roof was th¡n at stage rJ and
very thin at Stage f6.(Figs. 104 and 105).
The neural tube wâs separated from overlying ectoderm by neural
crest ceìls in the braln region at stage rJ, and by somitîc mesoderm and
neural crest cells over the braìn and somite areas by stage 16. The notochoid
was in contact with neurar tube în the regions of the somites,
protosomites and unsegmented mesoderm but not in the brain or caudal
âreas.
Somite development was normal,
.
with no reductlon ín volume and no
cys ts or hemorrhages.
Posteríorly, Hensenrs node had given way to a recognizable taìl_
bud. This was associated with the formation of the protonotochord,
fused mesoderm, and the tail-bud contribution to the neural tissue of
the caudal region. The primitive streak was much shorter than în
Stage .11-f2.
. In Stage 1l embryos, with an open posterior neuropore, an" iup".-
ficíal neural folds (deríved from neural plate) could be traced down
from above,othrough continuity of their future lumen with the lumen of
the closed neural tube. Deep to this was canaljzed neural tissue
(derived from the tail-bud) with no singre rumen. There was however no
clear llne of demarcation between these two sources of neurar materiar.
Neural tissue derived from the taîr-bud could be traced up to the proto*