XSLT: Want to merge data from 2 XML files

I am trying to develop an XSL stylesheet that will spit out XHTML using information from 2 separate xml files.

One XML file contains entities like this

The other XML contains entities like this

I can cut and paste the entities from the first XML file into the second file and get the output I want using the following:

My question is how to do this without having to manually merge the two xml files together. Can I get the stylesheet to read in the required data from the first file before processing the second file?