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The volume of the spine was measured in 9 embryos from 8 to 31 mm crown-rump length (complete series of sagittal sections). Spine morphometry was performed by planimetrical point counting of horizontal projections on a 5 mm square grid. Total spine volume was integrated by multiplication of the thickness by the area : V = t ET=1 Si. The integrated volumes (including the base of the skull around the foramen magnum) were aligned on the diagram semi-logarithmic volume v.s. linear crown-rump length. The correlation between the spine volume and the total weight of the spine is very high (r=0,94 ; p<0,01). The spine growth of the embryos during the post-somitic phase corresponds to the general laws for this period (particularly acceleration in the second half), one of the most interesting for morphometry during the uterine life. The vertebral morphology is perfecting between the two extremities of the observed period with a nearby adult disposition at 31 mm. Datation of the 9 embryos was determined from their C-R length by means of the table published by MOORE and al. (1981) from 641 staged embryos of the Carnegie Institute, thus establishing their stage with actual admitted criteria. There was no important variation of the unique spine curvature during the postsomitic phase. Linear measurements of maximal width on the entire embryos and their spine were determined from the total number of sections and those where the vertebrae could be observed. The two widths reported to crown-rump length, drew linear curvatures with a slight irregularity, emphasized by plotting the values of three indices. These variations could be dued to the imprecision in section thickness and to the individual variation during the spinal growth for this embryonic phase. In contrast with linear data, the morphometrical method applied to the spine volume has proved to be very effective in quantitative studies for embryos of the post-somitic phase.
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