Using elements inside XSLT file

I have a XML file, which contains itemid-elements, e.g.:
<itemid>3</itemid>
<itemid>12</itemid>
Now I want to convert these IDs to the corresponding name via XSLT. I
thought I could do it this way (XSLT):
<xsl:apply-templates select="itemid" />
<xsl:template match="itemid">
<xsl:value-of select="itemnames[itemid]" />
</xsl:template>
And I'd like to have this itemnames-element also inside the XSLT file
(rather than another XML file):
<itemnames>
<item>chair</item>
<item>table</item>
<item>cupboard</item>
...
</itemnames>

But it doesn't work this way because the XSLT processor searches the XML
file for the itemnames-element but it is inside the XSLT file. Is it
possible to point to the itemnames-element inside of the XSLT file? How?

Thank you in advance!

Max Evans