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

I l5
l'/hen neural closure was assessed, only embryos with neural tissue
(after St¿ge 6) could be incìuded (Hamilton, 1952). ln Table 26 and
Flgs, 18 ê 19, closure of the anteríor neuropore and rhomboîd sìnus can be
followed from 26 to 72 hours (Stages 7 - 2O'). The open braîn defects,:.regarded
as arÌsing by non-closure of the anterior neuropore, were only clearly
establ ¡shed in groups 30E g 42E, with one ,pont"n.ou, defect ln group 4ZC
(nig. zo)
Regular cord defects, regarded as arising from a tr¡angular rhomboid
slnus, coexist with an open rhomboid sînus as the position of the rhombold .l
slnus changes wlth lncreasing growth of the embryo. Open cord defects were
recognlsable in groups 18E, 30E, ê q2E, with spontaneous exarñples in groups
18C, 30C, E 42Ci in Fig. 20 they are subdivided inro regular and irregular
les lons.
Figures 21-J0 show camera lucida drawíngs of the typical changes in
embryos of the collected series:
St. 9 - at the time of windowing (0C 15)
St. 11 - open anterior neuropore and cysts (l8E 9)
St. 1B - open brain defect and anophthalmia (42E'20)
St. 13 i normal oval rhomboid sinus (l8c zo)
St. l3 - abnormal triangular rhomboîd sinus (l8E 6l)
st. 15 - early regular cord defect (30E 25)
St. 19 - later regular cord defect (4iE l)
St. 16 - early lrregular cord defect (lOt 73¡
St. 17 - later irregular cord defect (4ze 52¡
St. f5 - large cyst of caudal resion (3Og 3Z).