![](/drem/stage21/labels2/S41L.gif)
![artifact space(s), cerebral aqueduct (longitudinal section), commissure in roof plate of mesencephalon, fiber tract, head mesenchyme, osteogenic layer, rhombencoel (fourth ventricle), subarachnoid space, surface ectoderm, trochlear nerve (CN IV)](/drem/stage21/Z0/S41N.jpg)
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Carnegie Embryo #4090 | Location: 3-5
Keywords: artifact space(s), cerebral aqueduct (longitudinal section), commissure in roof plate of mesencephalon, fiber tract, head mesenchyme, osteogenic layer, rhombencoel (fourth ventricle), subarachnoid space, surface ectoderm, trochlear nerve (CN IV)
Source: The Virtual Human Embryo.