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

t69
ln both embryos the volume of neural tÌssue was so reduced that
somitic ñesoderm encroached on the midlìne, dorsal to the les¡ons where
they were covered by ectoderm. This again suggested that the dorsal
contrlbution to the neural tube (derived from neural plate materîal)
was considerably reduced in the area of the lesions (Flg,. 77) .
Examlnation of somitic mesoderm în one embryo (SOf lü revealed some
reductlon in volume at the protosomíte and unsegmented mesoderm areas
(though not elsewhere) with a diffuse arrangement of cells and some
cystic spaces (f ígs. 77-8Zl ... "r
Unsegmented mesoderm was in contact with neural tissue in one
embryo (30E l!) because of the encroachment of somitic mesoderm across
the midline dorsal to the lesîon
The.lesions in these two embryos thus appeared to show:
a) reduction of total neural volume
b) marked reduction in the neural plate contiibution, but faîrly normal
ta I I -bud contribution
c) early maturatîon of the tail-bud material
d) formation of normal cord from tail-bud material in the caudal
reg i on
e) exposure of the central part of the lesion, but ectodermal cover
above and below this
f) encroachment by somitic mesoderm ôcross the dorsal aspect of the
lesion where ectodermal cover was preserved
9) some reduction ín the local volume of postsomitic mesoderm
h) the occurrence of cyst¡c areas within the local somitic mesoderm.