horizon

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Related to apparent horizon: visible horizon

horizon

 [hŏ-ri´zon]
a specific anatomic stage of embryonic development, of which 23 have been defined, beginning with the unicellular zygote (fertilized egg) and ending 7 to 9 weeks later with the beginning of the fetal stage.

horizon

[hôrī′zən]
Etymology: Gk, horizein, to encircle
a specific stage of human embryonic development determined by the appearance and ultimate formation of certain anatomical characteristics. The classification comprises 23 stages, each lasting 2 to 3 days, beginning with the fertilization of the ovum and ending 7 to 9 weeks later with the initiation of the fetal period of intrauterine life.

horizon

any layer of soil that is distinguishable when soil is examined in vertical sections.
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