File:Frazer1928 fig03.jpg

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Text-fig. 3. 16 mm. stage

Position of structures, indicated as in last figure. Section through isthmus: fourth nerve decussating in roof, t.s. translaminar groove, other references as before.

The section shows (text—fig. 3) the early result of the growth of the basal lamina. The intralaminar sulcus is being pushed down in the side wall and is being invaded by the groups of association fibres. The nerve is now cut in decussation in the roof.

The section at this stage, then, shows considerable modification in the form of the cavity, with lowering and closing of the intralaminar sulcus and the beginning of a new secondary “translaminar” groove higher up, dividing the basal lamina into upper and lower parts. The whole wall, however, is still composed only of basal tissues, in which the nerve decussates in the roof and an increased area of association fibres lies in the lower part.

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Frazer JE. Development of the region of the isthmus rhombencephali. (1928) J Anat. 63: 7-18. PMID 17104212

Cite this page: Hill, M.A. (2024, June 19) Embryology Frazer1928 fig03.jpg. Retrieved from

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