Slide 16 - Tendon, in longitudinal section.  If the tissue was fixed while the tendon was under stress, the collagenous fibers will be extremely straight in longitudinal sections, with the thin, dark, elongate fibroblast nuclei lined up in parallel rows between the fibers.  Extreme compression of this sort is a diagnostic feature of tendon.  Often the fibroblast nuclei seem to be lying in tandem, with 2 or 3 of them in a chain formation.  If your piece of tissue was not under tension when fixed the collagenous fibers will be less compact and the cells less compressed.