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

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249<br />

6.6 pEVEL0PMENT 0F rH!_¡Ho|4glc R00F<br />

Changes in <strong>the</strong> structure <strong>of</strong> <strong>the</strong> rhornbic ro<strong>of</strong> were also evalu<strong>at</strong>ed for<br />

Groups I - lV. They are presented, toge<strong>the</strong>r w¡th <strong>the</strong> norphology and levels<br />

<strong>of</strong> neurâl defects (from Section 6.2), in Tables 43 - 46. and Flgs. 103- I11.<br />

Tables 43 - 46 show th<strong>at</strong> <strong>the</strong> rhor¡rbic ro<strong>of</strong> undergoes progressive<br />

th i nn îng after neural closure:<br />

Stages l0 - 11+<br />

Stages 12 - 15<br />

Stâges 16 - 17<br />

Stages 18 - 20<br />

thick<br />

thin<br />

very th¡n<br />

membranous<br />

The choroid plexus <strong>of</strong> <strong>the</strong> fourth ventricle is not present before<br />

Stage 18 (f¡S. lO9 ) considerably l<strong>at</strong>er than <strong>the</strong> first appeêrance <strong>of</strong><br />

myeloschîsis and myelodysplasia. ìlîthin each g¡-oup <strong>the</strong>re is no difference<br />

in rhombic development between experimental and control embryos. <strong>ln</strong> this<br />

ser¡es <strong>of</strong> chick embryos, <strong>the</strong> form<strong>at</strong>íon <strong>of</strong> open neural defects cannot be<br />

secondary to excessive pressure within <strong>the</strong> cerebro-spinal fluid system.

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