Fiducial points & contours

 

Fiducial points are points on your specimen that you mark to help you align subsequent sections. You may place fiducial points or trace fiducial contours. The criteria are the same.

Fiducial points are points present in all sections of the structure you are reconstructing. If the tissue has a cut edge, a point along this line can be a fiducial point. Other examples of good fiducial points include points along the central canal of the spinal cord, the longitudinal fissure, or the aorta in transverse embryo sections. Generally, any structure that runs longitudinally through the entire structure you have sectioned lends itself to the placement of good fiducial points.

 

If there is no structure present in all sections, as is often the case, we recommend to mark fiducial points that are also found on the next section. As a result, each section is matched with the tracing of the preceding tracing, rather than with the first tracing.

 

The best placement of fiducial points is done by selecting the points at a low magnification, then going to a higher magnification to adjust the placement of the points as accurately as possible.

Note that the alignment of sections is a bit of a subjective process. Fiducial points are simply another tool to help you do it as accurately as possible.