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

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6.8. EXTENT OF THE OVERLAP ZONE
The overlap zone is characterized by multiple accessory.canals
wlthln the tail-bud nater¡al, lying deep to a closing or closed tube
derlved fron neural plate material. Even without accessory canals ìts
presence is revealed by asymmetry of the definitive neural tube derived
from both sources (Figs. 51 - 60).
Uslng this asymmetry to lndicate the extent of the overlap zone, the
numbers of sectlons containing neurêl plate material and taíl-bud materiaì
were counted în each region of Group lll embryos. Values were expressed ås
percentages of each region and of each whole embryo .at Stages 13-,l6,
coverlng the developmental period in which the overlap zone ís most prominent.
The results could not be expressed ¡n terms of somite levels as the
definitive number of èomîtes has not differentiated at Stages lJ-16.
Group lV embryos could not be included because the overlap zone ís
obscured by complete fusion of the two sources of neural material after
Stage 16 in the controls and în experimental embryos without neural defects.
Tables !l - 54 show the percentage lengths of neural plate material,
tai l-bud material and the overlap zone ln Group lll
embryos, rearranged
into four catçgories:
Stage 13- 16 control embryos
Stage 13-16 experlmental embryos wîthout neural defects
Stage Il-16 experimental embryos with myeloschisîs
Stage 1l-16 experimental embryos wíth myelodysplasia ,
Figs. 120 - 123 compêre the lengths of overlap zone with the lengths of
neural defects in the four categories. They show that the length and distrlbut¡on
of the overlêp zone in myeloschísls closely resembles lts length