<p>It seems to me that links are best not included in <em>excerpts</em> (of course, they do make sense in a full wiki).  I think they should not be included for the following reasons:  </p>

<ol>
<li>Links don't work in excerpts.  For example, you cannot click on them to navigate to the indicated page.  </li>
<li>They are hard to read.  It would be cleaner to put, 'See the corresponding Wikipedia page' than (say) <code>https://en.wikipedia.org/wiki/Normal_distribution</code>.  (I'm not necessarily arguing we <em>should</em> put 'See the corresponding Wikipedia page', only that it's easier to read.)  </li>
<li>Our general policy for excerpts is to keep them as short as possible while still covering what needs to be covered (see: <a href="https://stats.meta.stackexchange.com/q/2848/7290">What is the optimal length &amp; level of detail of tag wiki excerpts?</a>).  </li>
</ol>
