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

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ì58<br />

One embryo shows ðn open brain (with a short upper beak), which can be<br />

compa red to rhe same defect <strong>at</strong> 72 hours (f¡g. Z3 ).<br />

Skeletal stain<strong>ln</strong>g <strong>of</strong> <strong>the</strong> experimental and control embryos revealed<br />

three types <strong>of</strong> vertebral defects:<br />

a) sp<strong>ln</strong>a biflda occulta (with no external neural defect)<br />

b) sp<strong>ln</strong>a bifida mênîfesta (associ<strong>at</strong>ecl with myeloschisis and myelodysplasia)<br />

c) reduction oi irregularíty.<strong>of</strong> <strong>the</strong> lumbar, sacral and caudal<br />

vertebrae. F.igs.43-46 demonstràte spîna bifida occul ta, spina blflda<br />

manifesta, rumplessness, and lumbo-sacral irregularity in four cleared<br />

emb ryos .<br />

There is not full agreement on <strong>the</strong> number <strong>of</strong> vertebrae in each<br />

region <strong>of</strong> <strong>the</strong> chick spine, because <strong>of</strong> <strong>the</strong> difficulty in assigning<br />

transitional vertebrêe to a particulãr region. The control embryos in<br />

this study general ly possessed:<br />

l4<br />

cervi ca I vertebrae<br />

7 thorac i c vertebrae<br />

4 I umbar verteb rae<br />

2 sacral verteb räe<br />

6 (5-7) fused caudal vertebrae<br />

6 (5-7) free caudal vertebrae<br />

4 (3-5) pygostyle segmenrs.<br />

Table ll<br />

and Figs. 37 and JB show <strong>the</strong> numbers <strong>of</strong> experimental<br />

and control embryos with three recognisable vertebral defects -spina<br />

bifida occulta, spina bifida manifesta (enclosing <strong>the</strong> Open neural defects),<br />

and deletîons <strong>of</strong> whole vertebrae. From Fí9.J/ ît is apparent th<strong>at</strong>:

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